Having an issue with my brakes (non-ABS). Replaced master cylinder because of a sinking pedal. Really nasty inside. Bench bled it and it worked fine for a week. Then started getting low pedal. Decided to bleed the system, since it needed flushing anyway. First two (RR and LF) went well. However, couldn't get any fluid or air out of LR and RF. Heard some noise around the LF caliper like air, but no leaks were visible anywhere. Could my "assistant" have damaged the MC by going to the floor during bleeding and would that affect only these two wheels? Any other ideas? Thanks, Dave