Currently I use http://www.alldatadiy.com/
(annual subscribtion $19.95). Not too bad, but sometimes incomplete. Until the official manuals are made available, that's all I got (or help from sites like this, when I can get it, but not very much information available to us on R129's right now). I'm VERY annoyed at Mercedes for not making those manuals available!!!!!! That car is 10 years old now, things are starting to wear and I would like to do some of the 'fun' stuff myself.