Avoid East Main Automotive in Northboro, MA.

Cheaper than others, but questionable parts and service.
They tell you to bring in the car early, then by the end of the day, they call and say they don't have time to look at it until tomorrow.
Then another day to order the part and another day....you get the pic. No loaners either.

One time I dropped the car off the night before, and on my way out, I stopped to peer inside the window of another nice benz in the lot, and the next thing I know this crazy man from next door comes out in his jammies, screaming and swearing and saying that he's gonna call the cops and have me arrested for whatever...!! This is like white trash Mercedes service!

I've gone to Hatch and Sons ever since, except for a few minor jobs that can't be screwed up too much (when I'm a little light on $$). Then I go to Grafton Foreign Motors in Grafton (duh). For Saab service, Patrick is the best. General service on Mercedes, good too. Not too cheap, not too expensive.
Has loaners too.