2012 Ford Explorer brakes problems

The left rear wheel began making a loud squealing sound (break pads) and when vehicle was at a complete stop, a large cloud of smoke was radiating off of the left rear wheel. The wheel was removed and the brake pads were stuck against the rotor. The brake pads are fairly new (replaced in february 2015). The caliper was removed and a retaining bolt was broken off/stuck inside of the caliper mount. The piston was pushed all the way inside of the caliper and would not extend out. The caliper was leaking brake fluid.

Had to have rear both rear calipers, rotors, and brake pads replaced because calipers were hanging up causing the brakes to drag. I also noticed smoke, could feel heat, and smell hot metal coming from right rear wheel on or around 6/14/15. I also noticed the same on 6/26/15. Dealership where I had vehicle repaired said that the left rear brakes pads were worn out, the right rear pads were 2mm from being worn out. Also both rotors were warped and discolored.