Originally posted by: AStar617
The E39 540i is arguably the most perfect realization of the sport luxury sedan, by many accounts. If I didn't end up buying my current home rather unexpectedly, I'd own one a Steptronic right now instead of my current E34. :beer:
One thing to point out: it's not specifically the 8, all of these cars will require higher than average upkeep costs. Between consumables like my Redline synthetic oil, premium fuel, appropriate tires, plus brake rotors that seem to wear nearly as fast as the pads--and nevermind when something actually breaks--it's always the total cost of ownership that gets you in the end. But almost every car save a handful in the bland Camry/Accord range will sound like a horror story if asked to point out every known problem with them. Just know what you're getting yourself into. It's a very rewarding experience, but you gotta pay to play
Some other general BMW gotchas, not specific to any model:
- The interior leather dye (and in some cases, the leather itself) tends to wear quite easily. IIRC, BMW makes touch up kits for guaranteed color matching, but actual cracks/rips/holes in the surfaces can be more troublesome.
- You might be confused to realize that many modern automatic BMWs (and possibly older ones?) don't have a transmission fluid dipstick under the hood. This is because BMW's "lifetime transmissions" are sealed; both the fill and drain plugs are under the vehicle and require it to be on a lift to access. BMW dealers will not replace your transmission fluid, regardless of your service history. This does not mean that they have some magical ATF fluid that will make your gearbox last forever, or that they guarantee anything like that. Take your car to a reputable tranny shop and get the fluid changed outside the dealer every 60k, the way you would on any other vehicle.
- BMW used to be good about prewiring their cars for options. Adding a 6-disc Pioneer changer, factory alarm, or car cellular phone (heh) to any E34 like mine is as easy as connecting a harness and maybe a few screwdriver turns. However, if you want navigation, buy your car with it. None of the newer nav-capable cars are prewired for it unless it's ordered as an option. I have the BMW-official procedure followed by dealers for when customers want to retrofit a car with nav. It's not pretty, something like 8-10 hours for 2 people to do. The good news is, upgrading your existing BMW nav unit from one level to another (Mk I thru Mk IV) is as easy as stated above--disconnect the old brain and head unit/bezel, and connect the new ones.
- Retrofitting factory LED tail lights and HID headlights on these can also be problematic due to improper application of seals... these are some more items that are better purchased with the vehicle.
- Keep up to date with recommended service intervals. Inspection I and II aren't cheap, but hurt much less if you are handy and have a decent set of metric tools.
Regarding the S62-powered E31, it should be a piece of cake considering this engine was
successfully shoehorned into an E30 M3 
Another fun fact: while a true M8 never made it past the test mule prototype stage,
guess where a future evolution of its S70 engine ended up?

A detuned version is found in the 850CSi--in fact, the original paperwork (and VIN decoding) identify every 850CSi as an "M8".
But I digress.