This is getting really frustrating. New master cylinder (again), bench bled, bled wheels in order, RR, LR, at this point the pedal is getting firmer, RF and the pedal goes to the floor again, LF no help. What on earth could cause this? Why does bleeding the front cause the system to go flat? This is the second time I've been through this; I thought my new master cylinder was bad so I got another one, and same problem.