Listen closely: The caliper is sticking because the brake fluid is contaminated with water. The inside of the caliper has rust and corrosion inside causing it to stick. It's important to have brake fluid completely flushed and replaced every 6-8 tears maximum regardless of the miles on the car.

People don't realize this but their master cylinders are vented to atmosphere to operate properly. Brake fluid, no matter which type sucks up moisture from the air like a sponge. All the brake lines are inexpensive soft steel tubing and the calipers are usually cast iron. Both of these metal types rust and corrode easily. The pistons inside brake calipers are at the end of the line for the moisture contaminated brake fluid runs.

A new re-manufactured brake caliper will fix your problem only of you get the brake fluid flushed. You're going to have trouble with the other three calipers if you chose not to heed my warning.