@alcade @RehnSturm256 @matrix Some pistons have to be rotated when compressed. If brute forced by a retard, the piston will be damaged. Some others, such as the ones on some Mercedes, aren't supposed to be compressed manually at all. They're supposed to be compressed by the ECM, and failing to use the ECM could damage them.
More often than not, however, calipers fail because people wait too long to replace the pads and the pistons overextend and start sticking.