George,

I agree it's pretty coincidental that you've encountered this phenomenon on both rear brakes; however, there's no question that the pistons that contacted the greater-worn pads are hanging up in their bores, and need to be rebuilt.

__________________
"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo