MBcoupes.com is an excellent list for later coupe owners - my experience is with the 380/500/560SEC section where Satish Tummala rules as an experienced owner who recently transplanted a 32 valve V8 MB motor into his 560SEC. There's a substantial focus on performance enhancements as well as regular repair information. Of course, most of the SEC data applies to the 380/500/560SEL also.
My piece on replacing the injectors in the 117.968 engine appears there.
http://www.mbcoupes.com