I've had 2 M5's in total ;
Daily Driver 1992 3.8 with 164k from March 2000 to March 2002
1 EDC damper at front. Probably failed as I'd bought a new house and had to drive on the sand as the builders completed the other houses.....approx £700 fitted.
Radiator........not too costly
Gearbox leak - simple fix with a new gasket.....
1995 6 Speed 96k now from March 2002 to present
Daily Driver until July 2004
2 front springs (1 broke and caused MOT failure, so both replaced) less than £200 all in if I remember right.
Air conditioning condenser replaced £600
Rear axle subframe bushes - fairly cheap to buy - a pig to replace.....
Think that's it, other than usual service items. Look after them and they'll look after you.
Mark