Why won't my brake system bleed the air completely?

What is your question?

I changed the master cylinder and then I tried to bleed the brakes from RR LR RF LF but the system is still has air. Sometimes it's not putting out any fluid at the bleeder points. A soft pedal has been a problem for years now. After changing the master cylinder it has no front brakes and very little rear brakes. The MC was bench bleed before being installed and both front brake hoses were changed.

How long has your 2001 Ford Mustang had this problem?

Years but recently has gotten worse