Interesting post...
It got me thinking...
My sons 88 300TE is very "whiney" from the front of the engine when he starts it from cold... Could that be the belt tensioner too?

Also, looking at the pic SteveBFL posted, what is the part with 31 and 42 attached to it?
I have one of these, that the PO included, but its just the lower part of that Assy... the threaded rod with the odd looking elbow and wrench type bit on the lower end.
What does it do?
I am missing the parts 31/42.

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2009 Mercedes ML320 Bluetec