Caliper rebuilding is quite easy. Use a blow gun with a rubber tip on the brake hose fitting hole to push the piston out, put a block of wood in the caliper bridge to catch it and watch your fingers! When removing the old seal and boot, use a plastic or wooden pick or you will gouge the bore and cause a leak. Use crocus cloth to clean the bore and steel pistons up, replace if they are pitted badly. Brake fluid or a slicone lubricant like sylglide should be used to assemble it back together. You should be able to seat the piston completely easily by hand if you rock it gently while pushing down. Use a block of wood to tap the new dust boot in place.