Caliper Disassembly (Rear Disc Brakes): Inspection
WARNING: This page does not describe the selected car, but rather 30 other vehicles, including the 1998 Pontiac Trans Sport, 1998 Oldsmobile Silhouette, 1998 Oldsmobile Bravada, 1998 GMC Yukon, and 1998 GMC Suburban. However, it is still accessible from the selected car via links, so may be relevant.
Inspect the piston for scoring, corrosion, and damage to the chrome plating. Replace it if any of these conditions are found. Inspect the caliper bore for scoring, pitting, or corrosion. Use crocus cloth to polish out any light corrosion. Replace the caliper if the corrosion cannot be removed.