jmohn
I can recommend Al at CPT.
www.gocpt.com
He's done good work on my A8. Throw out a post on the D2 forum in AudiWorld. You'll find other S8 owners.
Not sure of any known problems with the 02 S8 but the earlier model A8s (mine's a 98) had transmission problems and control arm issues. The engine is pretty bulletproof. $13K is a good price. Good luck.