I've got an M810 Saint caliper on my DJ bike which is super old. It's at least 7 years old, maybe 10 (can't remember which one I replaced) and it was used on my DH bike until about 2015. I've been running it on my DJ bike since then and I went to rebuild it when it was time for new pads + a bleed as the pistons were a little sticky.
Split the caliper, removed the pistons, cleaned everything, re-assembled, bleed, new pads, rode it, all no worries. Now 2 weeks later I've found that the pads are contaminated as all the pistons have a tiny leak.
Is it possible that after so many years of abuse, the grime and gunk around the pistons was the only thing preventing them from leaking after having worn down the tiniest bit? Or have I cocked something else up? I'm 1000% sure it's leaking from the pistons, I didn't mark, scratch, or score or part of the pistons or caliper when removing and cleaning, and the pads were new. Not sure if I try replacing the current pistons with ceramic pistons from a broken Zee caliper I have, or just buying an entirely different caliper.