I've been dealing with Rick at Eurotech, in Stafford, for years (Eurotech, A Mercedes Benz and Volvo Sales and Service Center). I first met him about 10 years ago when I bought an MB S class that had a fan problem; local dealer wanted $300 just to look at it, and said they were going to replace the fan, etc., for about $1200; Rick told me how to check it, and the part cost me $150 - he was dead on in diagnosing it, and a good bottle of red wine was well worth his advice.
When I took the -6 there, he didn't want to touch it at first, but once he realized it was just an AMG in disguise, he had no issues with it, and has been my go to guy since.
For those close to I95, he's just off the exit for Stafford Airport - tell him I sent you.

Kevin Long