If he's buying from a dealer, they can run a VIN printout and show all work done at BMW facilities. He should ask to see it, not just maintenance records.

Can your brother DIY? Doing the little things really help on these cars, as you probably know.

Suggest he check the For Sale section on M5Board to get a feel for pricing. IMHO its worth paying a bit more for good maintenance.

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I LIKE OLDER BMWS, PLEASE HELP ME:
Fern Green 99 M3, Conforti Shark Software, Conforti CAI, Dinan Exhaust. Stamped LTWs, 235x40 square, OE Hella heads, ///M Pedal Kit, Clear Corners, OEM Rear Spoiler, CD43 stereo. MRegistry listing here.
Le Mans 2002 M5, Black/Titanium, Rogue SSK, Dinan exhaust, PSS9 coilovers, Euro rotors, iPod integration. MRegistry listing here.