My 06 M5 was pretty solid, couple little things.
My M6 that I have know gave me SMG issues.
The awesome thing is when it happens it's without any warning at all!
Mine was the SMG pump and lines and throw out, also I lost an ionic sensor that was pretty awesome as well
Really really look into the service history. See if it had the Pump changed, there was some sort of free service or recall for the pumps.
M6 interlogos blue on black
Kw V3's, gt exhaust fibre tips, 20 inch alloy technic B9's (20 lbs) pzeros, gloss black grills, scoops/filters, v fibre lip, software.
2007 e60 525XI winter/commuter beater
2006 e60 M5 Silverstone (gone)
2003 M3, Oem CSL Trunk, Diffuser and centre console, Carbon fibre trim. (gone)
2004 330I ZHP, alcatara interior. miss that car