Anyone repair a read diff on a 300D. mine whines at highway speed. I changed the oil, no metal debris, so I figure gears should be ok.The carhas 190k.

 

Have you checked the rear wheel bearings? The rear differential should be OK for 300K+ miles.

 

I agree about the differential should last at least 300k.

At about 300k I had my rear wheel bearing go. The way to test it is to jack it up and spin the wheel. You should be able to tell where it is coming from.

Warning do NOT (that is never ever ever) try to replace the rear bearing on this Mercedes. I learned the hard way. After about 17 hours of trying to remove the bearing (I had replaced the fronts and they are really easy), I learned that you can't replace the rear bearings. Why> because there is a compression fitting that compresses against the rear bearing when they screw the nut on. I tried gently sawing this (very hard to get a grinder in there to begin with) and it never broke....
Ok, the moral of the story, you must buy the whole rear trailing arm. There are two bolts. Buy them on ebay or your local junk yard..

Scott