The only MB independent in the Georgetown that I know of is Carey's. I've only used him once but he did a good job diagnosing a bearing noise in a 190D and he fixed the problem for a reasonable price. My wife also used him for repairs on her W113 280SL in the 80's - no problems reported by her. There is also an independent in Camden-Wyoming and of course the dealer in Milford if you really need help badly.
Here is Carey's website.
I don't know if he knows anything about W124 4-matics - I'd suspect not since there don't seem to be many of them in the Delaware area.