Just as my car reached 100k I decided to change the fluid in the differential. I was told that Walmart synthetic 75W-90 would be fine. So I changed it and all seemed well. A few months later the car was on the highway and after about 1 hours worth of highway speeds I got a noise coming from the rear and I thought a rear wheel bearing was going out but the car made no noise around town. All seemed well until I got on the highway and after about an hour at highway speed the whining noise came back, so I decided I needed a rear wheel bearing. None of the 3 M/B garages would be able to do it I was told by them.

In searching this Forum I saw several posts that said the whining noise could be caused by the type of differential oil used. So I thought I would give it a try and put in M/B hypoid oil 85W90. I just got back from a Fathers Day trip on the highway at high driving speeds and much to my surprise the noise had vanished on the to and fro trips. Thank you AGAIN to all members of this forum as you saved me by allowing me to keep this wonderful automobile.