How often should I replace calipers?
Most brake calipers do not need to be rebuilt or replaced the first time the brakes are relined. But after 75,000 miles, or seven to 10 years of service, the calipers may be reaching the end of the road. As the rubber seals age and harden, the risk of sticking and leaking goes up. via
Why do calipers stick?
The common cause for a brake caliper sticking is with the caliper piston and the brake hose. The piston has a rubber boot on it which lubricates and protects it. But if this rubber is torn, it will cause debris and rust to form inside the caliper which means the piston's sliding abilities will diminish. via