Stuck Caliper Piston

I second the motion to replace the caliper. I like to RV on the Oregon coast, and often stay right next to the water. I drive a 1-ton Diesel and always applied the emergency brake. A couple of years ago the dealer had to replace all my calipers because the pistons all were rusted to the point where they would not properly retract - never had anything like that in half a century of driving all over the country. The mechanics asked me if I was from Canada with their salted roads! Now I am careful not to leave the truck parked too long with the parking brake applied to reduce the probability of rust building up.