master won't work

I agree w/ 273. If you bench-bled it, then you verified it was moving fluid. What does "doesn't work" mean? Does the pedal sink to the floor? Do you feel no resistance?

I had a fairly new rebuilt MC fail once. A factory type 1-pot. Pulled the piston and found the lip seal was cut from a sharp corner in the bore. Looks like the rebuilders machined the bore and didn't round the edges of the ports.