Cleaning vinegar is stronger, as is week killer vinegar.
I just thinned a set of snap ring pliers to fit in the master cylinder. My set had a pair that matched so I sacrificed them to make one more usable.
Some of the F brakes have an o ring on the OD of the piston side pad. I assume it's to keep dirt out. I removed one of mine, the pad seemed to hang up because it was there. I also got a new aftermarket piston that hung up in the bore of two different calipers, I spent a few minutes polishing it with red Scotchbrite pad while talking to a neighbor. Now it slides in and falls out with no seal.