If you're still looking for a MB shop in Tucson I can recommend Diesel Master on Tuttle. The owner is Marty who has been taking care of my 560SEL since I bought it. Don't let the name mislead you, he handles ALL Mercedes, not just diesels. He ONLY handles Mercedes. I can recommend him. If you want a phone number, let me know (I don't have it on me at the moment I'm writing this.).
2002 ML320 (thereby making my 560SEL my "spare).
1992 500E, pearl black, 27,000 original miles as of 7/2003.
1990 560 SEL, black pearl metallic, sweetness to drive. Fully outfitted with driving countermeasures (Beltronics radar/laser detector and Uniden BCT-12 Bear Tracker scanner).
1985 Porsche 911 meteor metalic gray, a rocket to drive.
1988 Chevy Silverado pick-up (gotta have something to drive to the rodeo!)
1978 Corvette Indy pace car for show
1971 Opel GT for sentimental reasons