MBDoc,

That's what I thought, too ... piston appears to be moving smoothly (checked it) ... isn't it odd that BOTH rears would wear the same ... maybe any apportioning issue at the master cylinder?

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg