So, I was getting significantly greater outboard pad wear on the drivers side rear brake than the inboard pad. Hmmm. Lubed up the pins, checked installation of pads and headed out for a race at Road America. I drove like crap, somebody hit me twice in 100 yards, but otherwise the car performed well.
After getting home, I inspected the rear brakes again and found the the top pin attached to the caliper mounting bracket had broken off. Damn, I was lucky.
Replaced both brackets.