Before buying a new caliper or rebuilding this one you may want to try to clean it first. Others may chime in but here is what worked for me several times on both cars and motorbikes to fix dragging calipers issues. After removing the pads press the brake pedal to get the brake piston out to its almost max. BE CAREFUL NOT TO GO too far though not to pop the piston out of the caliper. Clean the caliper and piston with brake cleaner. If needed sightly sand the piston sides with a LIGHT application of 800 sand paper or ScotchBrite pad and clean it again with brake cleaner. Then lubricate the sides of the piston with some drops of brake fluid and push it back completely by using a clamp. I use the old pads in between the piston and the clamp to avoid damaging the piston when I push it back. Put the new pads and mount everything back together.