Not had an M5, had a 6-speed 4.0 V8 though, which isn't a million miles off.
Fantastic bits of kit really, in reality you're just looking for good history, as low as mileage as possible and for evidence that the car has been well looked after.
I've seen 220k examples selling for 2k recently - I went and looked at one and it was in fantastic condition really - they take the miles very well -
BUT they are expensive to maintain - they are not your run of the mill 5 series with a fancy engine. The real catch with the M5 is that if something does go wrong, parts prices for specific components can be extortionate, and with the labour requiring specialist attention, one major failure can be enough to undo the car's value completely.
You also can't run the car with a 'I'll get that fixed later' kind of attitude - if it has a fault, it really will need attending to on the spot as otherwise you could be letting yourself in for something worse.
My old 540i 6 speeder:
Great car to drive - and that was the long-standing impression left by mine on me, which was a little rough around the edges and had done 180,000 miles!
You want to buy one with a strong engine that runs without fault - as rebuilds are expensive - but if it's been cared for, it shouldn't be a problem anyway.
Other things:
- Transmission / Clutch - does it run well without any odd noises or judder?
- The classic front end wobble, with the E34's suspension and bushes wearing with age
- Shot water pump
- Oil and water leaks
- Loose steering, as the steering box can wear
- Window operation
- Rust
- Shocks
- Compression & general engine health
- Receipts!
There is a mine of info here:
http://www.m5board.com/vbulletin/e34-m5-discussion/
Find an M5 that's been thoroughly maintained and the guy wants like $17 grand for it (because that means he probably has that in it in maintenance alone). Look for one that is as OEM as possible, unless the SLS delete has been professionally done. Repairing the SLS right is almost always worth the money because of how it integrates with the nurburgring suspension. Really, if the M5 have MSystem turbines still on them, that's a good sign its a one owner garage queen. If it's got over 100k and the EDC dampers haven't been replaced, it's not worth more than $5k-7k, I don't care how clean it is....dampers are $2500 a fender endofstory. If it's been tracked, it's probably been wrecked or the clutch and drive train areas are worn. Open the hood, look for any DOT-R stickers. Run your index finger nail along the hood line by the windshield for indications of respray (if your nail catches, it's been sprayed). Look for stamps in the owners manual. Is the owner a old fart or is he a punky kid...usually the best sign on how the car's been treated. Is there cosmoline still all over the engine? Pay $266 for a PPI at a reputable indy...who will put the car on a lift, find origin of leaks, see if the diff's been opened up, oil pan plug stripped, guibo, use a pry bar to see if rear subframe bushings are shot, play in the center support bearing...plan $500 off price for each find. Look at the felt by the windows for cigarette burns, check rear fender area and lower skirts for rust bubbles, let the engine idle and use any sort of stethescope device on the valve cover for out of the ordinarty ticking or chain tensioner noise..look for sprayed coolant
