Getting disk brake calipers back together

[70herald]

Hi
I am trying to get a set of disk brake calipers back together and am having an frustrating time. One caliper seems to work however the other caliper just leaks lots of fluid.
I pulled out the pistons and it is obvious that the o-rings were cut when I forced the pistons in. Now I put a new set of rings in, and lubed it up and the same thing happened.
Both the pistons are nice and clean. The top of the piston looks like it was sand blasted. The sides (sealing surfaces) are very well polished.
The only thing that I could see with the caliper is that the o-ring has a little bit of wiggle space (width wise, depth seems right on) The o-ring seems to rotate slightly when I push the piston in, and then the edge of the slot cuts off the ring.
Is this normal (not the cutting off part, the width)? Anyone have any good ideas as to how to get the *!****! pistons in?

 

[martx-5]

It sounds like the area behind where the seal (square O-ring) goes (the groove) is corroded and/or has some dirt there. When the seal is in the groove, it should only stick past maybe .030". If it's rolling over, then something is causing it to stick out too far. Since one caliper is OK, I would have to say that the new seals are the correct size.