Some history on this: First time rear break locked up. Checked fluid discovered reservoir was distorted, guessing it's from the closeness to the pipe, and no fluid in res. more like mud. Replaced reservoir, flushed with copious amounts of fluid. Still locks up. Removed caliper. Tried to compress with C clamp. Still locked. Cracked open bleeder and boom caliper moves freely. Is there a check valve in this system thats not working? Need new caliper? Am I doing something wrong? Thanks for any help.