I have a drivers side rear brake caliper spare, as i fitted new calipers. Was working perfectly when removed from my car. Piston surface is in excellent condition and so is the seal.
It does however need new seals for the sliding mech, these can be had from else parts for around £12, it wasnt run with damaged seals, i needed to switch them over to my new calipers as i managed to pinch the new seals when fitting the caliper to the car! these seals are easy to change.
looking for £50 + p&P
Ian