Well, I too own a 16v now. I purchased a flawless 86 5 speed. I love it.
Anyway, my diff whines a little too. I think I will drive mine untill I have a problem with it. There is a diff for sale in the classifieds on the front page of the shop forum.
I have talked to Doc about this, he has rebuilt quite a few in the early days of the 16v. I think it is the nature of the beast.
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MERCEDES SPECIALIST 11 YRS