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
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
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.
2008 BMW 335i Coupe