When a caliper leaks or sticks, one option is a rebuild kit instead of a whole new caliper. Here is what a caliper rebuild kit is and when it makes sense.
What is in the kit
A rebuild (or seal) kit typically includes a new piston seal, dust boot, and guide-pin boots - and sometimes a new piston. It lets you refresh a caliper whose body is still good but whose rubber has failed; see torn dust boot.
When rebuilding makes sense
Rebuilding is worth it when the caliper bore and piston are clean and smooth - just the seals aged. It is common on older or collectible vehicles where a new caliper is expensive or unavailable; see rebuild vs replace.
When to replace instead
If the bore or piston is pitted with rust, a rebuild will not seal or slide reliably - replace the caliper (a loaded unit) instead; see why calipers stick. On most daily drivers, a quality reman or loaded caliper is faster and just as good.
Do it right
Whether you rebuild or replace, clean everything, use fresh seals and grease, bleed the system, and fit fresh pads on that corner; see slide pin service. Fit quality pads and hardware.