Did you replace the MC? I ask because the power brake ones should have a retaining ring where as the manual ones have a plate with a dust boot on it and an undercut to retain the push rod. My car is a manual brake car where the plate was no longer flat and someone left the remnants of of the piston seals on the shaft . This prevented the piston from returning properly and resulted in locked brakes after driving for a few miles because the compensation ports were blocked.
