I usually take my car to either..

European Car Doctors [Boston, MA] - look for Carmine. His shop is around Fenway Park.
61 Brookline Ave. Boston, MA 02115
617-262-5525

That's the closest shop to my apartment and I'm so glad!
He's a great guy though parts could be cheaper but I've got so many valuable advices and he has saved me lots of money by not telling me to replace a radiator when all i needed to replace was a clamp. (that's only one of them)

another great shop is..

Koko's Garage and Son [Cambridge, MA] Their shop is small but you see MB diesels mostly and a bunch of W126's and W124's..and also other MB's... a great shop too and great people!

651 Mount Auburn St. Cambridge, MA 02138
617-576-2757

Those are the only two I've used that have given me more than just great service. There is another one that I'd just avoid like a plague but I'd rather not mention here.

Good luck,

__________________
2008 BMW 335i Coupe