Hi, I have a 2001 Mustang Bullitt. My left rear caliper has been having issues. The outside pad has worn down and ruined my rotor, however the pad closest to the brake piston is still very well padded. My question is, what would be the difference between seized sliding pins and a bad caliper? How do I know my pin is seized? I had a bit of trouble unscrewing the screw that is screwed into the pin. Please help