An example of aging to ponder
One of the things that started me re-building calipers for people years back was the down & dirty front pad installations that guys would do(or have done) in order to complete Safety inspections. Common practice was to pull the pins, open the bleed screw (if it would move), force the pistons back with whatever would wedge in the gap, and finally, drop in fresh pads, pump the brake pedal and drive away.
Calipers would show up at my door once the mechanics and/or owner had agreed that something "had happened" when the new pads went in. How many long & boring stories can we tell about all the lingering rust and other nasty chemistry that gets dragged in past the dust cover groove when those pistons are pushed back. I've had to come up with some creative tooling in order to get some of those pistons to even think of moving again. Uneven movement will warp the rotor from only warming one side, etc. etc. And then there's always the phone calls about "how do you get that F------ dustcover to stay put. And many other moments of frustration; amen