A (mostly) complete guide on how to purchase the best 4-door sports car ever made.

BMW's M division has made quite a name for itself by taking cars, primarily leased by first-year CPAs and paid off by tenth-year CPAs, and placing exotic drivetrains where their significantly less dramatic stock engines used to be. Arguably the most notable and ubiquitous iteration of any M car ever is the universally praised '00-'03 E39 BMW M5.

The car you're looking at has room for 5 adults, a little more than 11 cubic feet of storage space in the trunk, dual-zone climate control, an 18.5 gallon fuel tank, and if driven responsibly, a return of 26+ miles per gallon on the highway.

It also has an engine with an independently controlled throttle body for each one of its eight cylinders, variable valve timing for both intake and exhaust cams, with more power under the curve than John Goodman, all of which revolves at a maximum oil-pump shattering 7000+ RPM.

And then there's the noise. This is what American muscle cars would sound like if they stopped ripping beer bongs and studied on the weekends. The distinct induction noise and refined exhaust note (especially with a straight pipe or muffler delete) combine to form a sound that is the embodiment of subdued chaos. This is the automotive aural equivalent of a UFC fight. Here,

There are two gearbox options: a 6-speed manual with a shift knob that matches your interior trim, and a 6-speed manual with a shift knob wrapped in leather. BMW took a page out of Henry Ford's book ("any color you want, as long as it's black") and opted to make this car a worldwide manual-only model, which, as far as decisions go, ranked somewhere between rebooting Top Gear in 2003 and the invention of the bacon cheeseburger. The gearbox is without a doubt one of the best manual units money can buy. Its throws, although a bit on the long side, are sniper rifle precise, with the forgiving learning curve of an air-powered pellet gun. Its long gears work with the engine's massive torque supply to turn a marathon highway trek into a race against the GPS' estimated time of arrival. Challenge accepted, Garmin.

The interior of the M5 is at the higher end of BMW's spectrum, featuring enough color and trim options to satisfy even the most peculiar and pedantic BMW buyer, also known as the average Saab owner. Its seats come as standard with supple leather, with an option for two-tone Nappa leather, with — get this — ostrich print. I didn't believe it until and got exactly that. It's not exactly a but it certainly allows the car to hold its own against other luxury saloons. Other interior/comfort options include a power rear sunshade with manual side shades and Park Distance Control System.

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NOT EVEN A MAYBACH HAS THIS!

The only notable audio system the car comes with is the one you control with your right foot — it's at the very least more satisfying, though much more repetitive and expensive to run. The actual Navigation/DSP/Premium Audio system that the car comes with has the fidelity of a can of expired cashews and the frequency response of a crying child. It's by far the worst audio system in a high-end car that I've ever experienced, but with the magic of the free market, it's made much, much more tolerable due to . Changing out the stock audio components aren't a suggestion, they're a condition of buying the car.

. BMW revamped the lighting system, adding HID bulbs, daytime running lights and halos, a new, thinner spoke steering wheel, as well as a widescreen 16:9 widescreen navigation display.

How much can I expect to pay for it?

The market for this car has reached its bottom without a doubt. You likely won't see these cars any cheaper than you do now by any significant amount, and you will see these jump in price in the coming years, for two simple reasons:

There's a strong resurgence of people looking for fast cars that deliver an analog driving experience.Only 9,992 North American examples were made throughout its 4-year production run. The E46 M3, by comparison, had nearly 4 times that amount. It's relatively rare car with an insane value per dollar.

To understand how much to pay for a specific example of car, I'll rank on a scale between 1 and 4, called the Car's Roadworthiness, Aesthetics and Performance, or C.R.A.P.

A 1-owner car with ridiculously low mileage, garaged exclusively. It has a full dealer service history and the owner is extremely OCD and sentimental about ownership. The car is flawless inside and out and has had all work performed by qualified professionals. The receipts for the maintenance and repair work completed are in chronological order in a 3-ring binder and possibly laminated, and all original materials are accounted for. This is a car that is devalued when it leaves the garage.

A car that has been maintained by its owner at or above the standards set by the manufacturer. The only thing keeping this car from being a 1 are some threadbare details or details that could use some reconditioning, due to wear and tear. Mileage is relatively low, but not so low that you might mistake it for a car left in storage since new. A low number of owners and mostly available service history let you know this car was cared for well by all previous owners. A nearly perfect car.

A car that is average condition for the age, with miles being fairly acceptable. This car may or may not have service history, but shows no signs of major mechanical or cosmetic damage. It will need some reconditioning to get anywhere close to a 2 in terms of appearance. The title is clean, but may have a larger number of owners with a questionable history. It'll require some more money after the initial purchase, but it's a solid foundation and warrants an in-depth look, if not an outright purchase after inspection. Most cars will be in this category.

A car that is a flat tire away from being totaled. This car will need major mechanical or cosmetic reconditioning to be presentable and drivable. This car may need to be towed, and may have a salvage title or major accidents in its past. Stay away unless you know what you're doing, or you want a parts car.

Is it expensive to maintain?

Well, noble reader, that all depends on what your definition of "expensive" is. The car's chassis, underneath its exotic "WBS" VIN code, is a regular 5-series chassis that any independent shop or backyard mechanic can work on without fear of breaking something irreplaceable. Body panels are plentiful and interchangeable between all E39 models, as are some components of the suspension.

Maintenance, however, can be where the exotic nature of the drivetrain makes a statement. The car uses , just like the . An oil change with filter can be upwards of $150, but thankfully, the oil is synthetic requires changing every 7500 miles, instead of 3000-5000, like most conventional cars on the road today.

A mostly complete guide on purchasing the Ultimate Driving Machine. Don't Panic.

Transmission and differential fluid don't have to be changed for 20,000+ miles, but when they do, they can be a bit costly, at more than $20 a quart. The preferred transmission fluid is , but more cost-effective alternatives, such as can be used instead.

Brake pads, as well as rotors, are proprietary and not interchangeable between E39 models, so you'll have to spring a $500 minimum for a quality brake job that's due every year or so if you're driving this car like it deserves to be driven. with replacements needed every 2 years, depending on driving style.

Spark plugs () can be bought for less than $6 each at any auto parts store, and installed just as easily as any run-of-the-mill mediocrity-mobile.

The various filters of the car (, , ) can be purchased through aftermarket companies that provide the OE part, without the BMW branding, and thankfully, without the BMW markup. All filters will cost approximately $130 to replace (parts cost), with a shop charging another $100 or so to install them all, if DIY isn't your thing.

A good estimate on general maintenance every year would be $1000 or less, and $2500 every 2-3 years for larger, more labor-intensive services.

What problems should I look out for?

Unlike other fickle supercars, the E39 M5 is built with longevity in mind, this is a reason that you can find several very high mileage examples still on the road today, despite the low total production number of cars made. Having said that, there are a few things you should check before purchasing a new-to-you M5:

A huge design issue that plagued the S62 engine was the secondary air injection system. The engine naturally burns a bit of oil (about .75 quart per oil change), and the unburnt vapor makes it way into the intake manifold and eventually the secondary air injection system, which is a system that allows the car to be safe, emissions-wise, from a cold start. When this vapor reaches the cylinder head, it solidifies and creates a blockage so hard that the only way to remedy the issue completely is to take the heads off the engine and drill the passages clean. This costs upwards of $2000, and it WILL happen again over a certain number of years and heat cycles. A good way of knowing if you have this problem is if you have a SES light (Service Engine Soon) illuminated, with a "Secondary Air Pump Low Flow" code.

Since this isn't necessary for the engine to function, there's a that makes the engine's computer simply forget that it needs to check this system. There have been no drivability or emissions-related negative consequences reported with this mod, though use at your own risk. .

This generally is an annoyance, since it makes the car sound like a beige Mercedes diesel wagon at idle (easy, there!), but doesn't actually harm the engine. The reason for the rattling is that the tolerances for the VANOS system allow for a certain amount of "slack." which is translated into an audible rattle when not revving the engine to high heaven. The remedy is a lifetime fix, made possible by — a full overhaul of all system components to the tune of around $1000. Whether it's worth it depends on how annoyed you are that your M5 sounds like a farm tractor.

The timing chain tensioner, after being used and abused with various different (non-OEM spec) types of oil, becomes sluggish and can seize, putting slack on the timing chain guides, and wearing down the chain itself, not to mention changing the actual cam timing. The tensioner is a , although a bit finicky. , and labor comes in at $200 for any independent shop worth their salt.

The car has two coolant temperature sensors, one in the engine, and one in the radiator. If one sense that things don't match up within a certain range, it triggers a check engine light. This, although annoying, is a great way to know if your thermostat is stuck open and making the engine run less predictably than what's ideal. and can be (again, finicky - lots of cursing involved), and at a qualified shop for approximately $150 labor.

Other than the mechanical issues, keep a close eye on the electronics, as they can sometimes suffer from faulty relays, causing some components to develop abnormal wear. These issues are not too common, but they are worth keeping in mind when purchasing an E39 M5.

Will it Baby?

Would you buy one?

If you had been following my series, you would've noticed this. I bought one, loved it, and now am searching for another to replace it in my collection. Life is hard.

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Who else has one?

None other than the Trans-continental record holder ( ) . He drove his E39 M5 From New York City to Santa Monica Pier in 31 Hours and 4 minutes on the road, and even . Something that can do an average of nearly 100 mph for more than a day straight is certainly something special, and definitely a reason for the E39 M5 to be on your short list of awesome lifetime buys.

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(Photo credit: Cars-Specs.com, Wikipedia.org, Bimmerfile.com, BMWblog.com, flickr.com, APiDAOnline.com)

is the founder of and writes about on the internet. He owns the world's cheapest , a , and he's the only Jalopnik author that has never driven a Miata. He also has a real name that he didn't feel was journalist-y enough so he used a pen name and this was the best he could do.