I noticed at the track this weekend that on the driver-side rear, the outboard pad was not making full contact with the rotor surface. It after a few sessions it wore so that it was getting full bite. I initially chalked it up to production variation.

After swapping them out, I see that the inbord and outboard pads have both worn at angles rather than parallel to the backing plate. So it seems its getting bound on a pin or I have a bad piston. How can I tell between the two?