They can be rebuilt but not by a novice. Replace it with a rebuilt unit.
You replace them!
just replace the whole caliper.
Replace
If the caliper is sticking or leaking it is possible to buy a rebuild kit and replace all parts that are worn inside. If the caliper has a cracked or broken housing then the unit can not be repaired and must be replaced.
You replace them. It's quite simple and involves only removing the brake caliper and caliper mounting.
Rebuild the cylinders on that caliper.
The best thing you can do is replace the caliper.
To replace a faulty brake caliper with a new caliper or a rebuilt caliper and assuming that is all it needs, a garage would probably charge you one hour of labor plus the cost of the caliper and brake fluid. Call your local auto parts store to get a quote on the brake caliper.
You have a leak in the caliper piston most likely due to rust which causes brake fluid to leak past the rubber seal. To fix, you have to either rebuild the caliper yourself or buy a rebuilt caliper from the parts store. If you buy a rebuilt caliper, it will come loaded or unloaded. Loaded = comes with brake pads. Unloaded = caliper by itself (no pads).
To fix a loose caliper on your car's brake system, you will need to first jack up the car and remove the wheel. Then, tighten the bolts that secure the caliper to the mounting bracket. Make sure the caliper is properly aligned and not rubbing against the rotor. Finally, test the brakes to ensure they are working properly before driving the car.
If the caliper is sticking or you can't get the piston pushed back in it's best to just buy a new caliper.
A brake caliper kit is a kit that allows someone to fix their car's disc brake caliper. It often includes all of the necessary hardware to complete the task as well as detailed instructions.