>>>>I think the piston in the brake caliper is sucked back by the brake master cylinder piston moving back as the brake pedal in released and has nothing to do with the caliper seals or discs.
Looking at the caliper piston when the brake pedal is released and you can see the piston moving back from the disc.
JR<<<<
Hi John
If you think about it, when you are bleeding brakes the old fashioned way & your assistant repeatedly presses the brake pedal, the brake fluid will be expelled on the down stroke & on the return stroke the fluid remains motionless, thus pumping fluid & air out of the system. If the master cylinder was responsible for pulling the calliper piston back, then bleeding the brakes would be nigh on impossible.
There is lots of information online that will confirm what I saying