A rebuild mainly consist of replacing a rubber o-ring(s) and getting a new piston(s). Honestly though when it comes to brakes, and other items that ensure your safety I like to get brand new parts. I believe you can go to any parts store and give them your old GSX calipers as a core and you might can get some nice new ones. Otherwise they will be rebuild ones that have been cleaned up. Also check your local Mitsu or Chrysler dealers and see how much brand new ones are going for. Just some ideas.