Larry,
I've only had one Mercedes and it "warped" every set of discs that its ever had - 2 or 3 in both front and rear. (I've never warped discs on any other car). Mechanic replaced them under warranty and replaced two calipers (used) along the way. This is over 80,000 miles with Ate and dealer dics. About 15,000 miles ago I rebuilt the rear suspension and put delaer rear discs & pads and they still warped - and BAD!
Last month I installed 4 new/rebuilt calipers & installed front discs and pads from my parts car (cleaned some of the rust off with brake clean) and they ran smooth and have stayed that way. About 1700 miles ago I installed new Balo rear discs with existing pads and the car is still stopping smooth as glass. I'm still amazed
.
So, my conclusion is that something in the calipers causing the problem.