Clean the brake caliper and piston with clean brake fluid or brake clean and dry them with lint-free towels or low-pressure air. Skip using gasoline, kerosene, thinner or similar solvents since they may be harmful after drying. Check the piston, made from phenolic resin and see that it is undamaged; if it has cracks or scores, put in a replacement piston and do not try to repair the wear by sanding or polishing. Use only the same type of piston, as because of differences in pistons, seals, seal grooves, caliper bore and piston tolerances, phenolic resin and steel pistons should not be used together. A light braking with a hone might help smooth the bore, but if the bore is corroded, rusted or scored or if polishing changes its size by more than 0.025 mm (0.001 inch), a new caliper should be used.