Just an update.
I brought the car to an indipendent mechanic that was not too happy that I brought the parts for him. And yes the Diff gear oil was half empty, dark and looks like never been change before. Got the Spark plugs replecaed with Bosch P+4.
Flex disc shows hair crack and he said wait another 10K, under the hood there are lot of plastic fastener broken, crack hoses al over, air filter housing could not close due to broken fasteners etc. I was wondering why MB could not get a better plastic components that have a better heat tolerance? Do they need to learn from the Japs??