I recently had the motor mounts in my 1991 560-SEL replaced. The originals had disintegrated. Prior to replacement I never detected any sound when shifting from neutral to reverse or drive. However, now when I do there is a "clunk " not one that would be categorized as severe; more annoying than anything else. I took the car back to the shop who replaced the motor mounts where they put it on the lift and while running had another person in the car shift in and out of neutral. There was a clunking sound coming from the drive shaft where it connected to the transmission and the differential.
The shop owner, who has quite a number of years with Mercedes before setting up his own shop, told me that the noise was something that was normal with the 126's and that it was probably being muffled by the buzzing sound due to the deteriorated motor mounts. I do have to agree with him about the buzzing sound that existed prior to their replacement.
I'd like to know any opinions that any of you might have of this. I don't think it could be from excessive wear since I only have 12,000 miles on the car. It could also be that I have not driven the car that frequently enough yto know if it has been there for a while