Motorcycle Repair: 85 FXRS Rear brakes locked up., rear brake caliper, rear caliper

Question
After 12 years in storage, I re-activated my FXRS. The rear caliper was locked open, (no braking action), so we rebuild the caliper, bled it and everything seemed fine. After about 30 stops The rear brake caliper locked closed. The pedal was all the way to the top. On the road and far from home, I opened the bleeder, got a lot of air, and the brakes released. I figured the air was due to boiling the brake fluid. After getting home and letting the brakes cool, I was able to pump up the brakes and get good pedal, with a little play at the top. All seems normal now, but haven't ridden it due to the idea that there might be something wrong with the master cylinder not letting the caliper release. Not sure what's going on?? Also am having a hard time finding a rebuild kit for the master cylinder at dealers or independent shops around Detroit.

Answer
Your master cylinder is probably bad. I would replace it instead of trying to rebuild it. Over time the cylinder in the master cylinder pits and if you try to rebuild it they usually leak and you end up replacing it anyway.
Good luck and happy riding
Mike