The piston seal itself is in a groove, on top of the bore of the caliper.
The seal isn't on the piston itself, having to go up and down in the caliper bore, like on the BUDD, or BENDIX, designed brakes.
The seal, seals up just fine, on the Kelsey Hayes brakes, with the piston installed in each bore hole.
I'd have to see a clear picture of what your working with.
Obviously, you must already have them disassembled for evaluation.
