the cups I am referring to are the MC cups. on a MC with some miles I like to keep those cups in that normal worn area when bleeding (not a dealbreaker but does extend the life of the piston seals). I would crack the line just upstream from the prop valve see what develops. does this valve have the pin that you pull out to bypass the proportioning? EDIT & a block of wood gives your helper more control over the pedal movement & on discs I like to have him pump it several times then with good verbal timing I open the bleeder on his last downstroke as this agitation gets the air out better but we ain't there yet, first we gotta find out what is going on.