what causes the brake piston to lock up, everything is mechanical and only require brake fluid to build pressure, so would the piston lock up, and how would you correct that without getting a new one?

 

Pistons tend to seize or lock up when the brake fluid is old, contaminated with water, condensation and rust. The O-ring piston seals become brittle and enlarge or swell up.

Brake fluid is designed to absorb a limit of water. This is why it is necessary to have the fluid changed every few years.
When a caliper starts to seize, the best remedy is replacement. Calipers and cups should be separated and rebored, eliminating the rust damage.

 

thanks for the info