I own a 1991 850iA, I founded the E31 Owners E-Mail List in 1997, and I wrote the E31 Buyers Guide that has been posted in this newsgroup several times. Here's my take:
I am instantly suspicious of E31s with extremely low mileage for two reasons. First, I suspect odometer tampering. Not accusing the original poster of this. I'm just saying that there *are* sleazy sellers out there. Second, even if the low mileage is genuine, that is not a good thing. Storing a car is an art and most people don't know how to do it. The original poster mentioned his 850 was under a cover in a carport. I have no idea of the climate where he lives, but if it's damp or cold that's bad. Moreover, storing a car under a cover can damage the paint as much as it can protect it. When a car sits idle corrosion can form inside the engine, acids can form in the oil, the rubber parts can deteriorate, and the leather can go to hell. And let's not forget bird and rodents.
If I was shopping for a used E31, I would MUCH prefer a car that has been driven regularly -- say seven to ten thousand miles per year. Given that most V-12 E31s out there were built in 1991 or 1992, we're talking cars with more than 100K miles. At first glance this is offputting. But the M70B50 powerplant features a VERY conservative design, with two valves per cylinder (which are self-adjusting), a timing chain instead of a belt, and a low compression ration. In everyday driving, a mature driver will seldom see more than 2,500 RPM. (Remember, the E31 is a Gentleman's GT, not a high revving sports car.) With regular oil chainges using good synthetic oil this motor will easily last 300,000 miles.
That leaves the ancillary systems -- things like the infamous DK motors, the dual fuel pumps, the dual batteries, the hydraulic system with brake accumulator, the sometimes-leaky intake manifold gaskets, and the ZF autobox. To be sure, in the E31 these systems are complex and expensive to maintain. But I would submit that making a half-assed attempt to "preserve" an E31 in your carport is just as hard on these systems as actually driving the car. For example, in a stored car it's almost certain the brake fluid has absorbed water and the entire braking system is rusting from within. Ditto for the exhaust system. In the air conditioning, the refrigerant also lubricates the moving parts and seals. (That's why the compressor defaults ON even with the snowflake button deselected.) When the car sits idle this doesn't happen and you're looking at a $2,000K rebuild.
Finally, a word on the E31's "collectibility." In my opinion, it's just not going to happen. If you look here, you'll see that roughly
23,000 E31s with V-12 power were built:
formatting link
Granted, only about 4,600 of those made it to the North American market. And after all these years I'm sure that some of have wrecked and some have descended into beater status. But if you want to buy an
850i or an 850Ci you'll still have plenty to choose from. So the scarcity that makes a car a collectible just isn't there. Might that be the case 20 years from now? Perhaps. But there are better ways to invest your money. See:
formatting link
Obviously, I'm biased. But I think the E31 is still worth owning, PROVIDED you go in with your eyes open. First and foremost, buy a car with a verifiable ownership and service history. Private sales are better than dealers (and, god forbid, wholesale auctions). Fewer owners are better than more. If the car does not have complete and detailed service records going back at least five years (ten would be better) look elsewhere. If you just gotta have THAT car, then substract at least $5K. In summary, it's better to pay $18-20K in a private sale from an owner with good records than it is to pay $12K at "Bubba's House of Used Cars." (Motto: "Buy Here. Finance Here.")
Once you own the E31 you gotta maintain it. Don't be fooled by the low purchase price. As 8-Series owners are fond of noting, even if you got a great deal when you bought it, it's still an $80,000 car when it's time to fix it. If you can't afford at least $5,000 per year for upkeep buy an Accord. Ditto if you live in some rural area where you can find a good shop.
Now lest you think I'm all about the buzzkill, I will say that the expense and the hassle are definitely worth it. The E31 is an amazing car to drive -- especially out on the freeway at speed. It's built like a bank vault and utterly solid and stable even at triple digit velocities. And you'd better be a friendly sort, because every time you stop for gas some car guy will approach you to ask about the car and to request a look under the hood. After all, everybody who cars about cars should own a V-12 at least once.