I've only rebuilt a brake caliper from a light plane, but it is the same principle. The kit is nothing more than a rubber seal, o-ring, and piston(optional). After you pop out the piston, check for rust and corrosion, clean the assembly then re-ring it and replace the rubber seal. 30 minutes max!

On my 850, however, I bought rebuilt calipers from FCPgroton, but the pistons were in worse condition than the original ones from my car. They were pitted from corosion. I would have rebuild them if I had the time.