Daily driver, master felt like it was going, 6 months or so ago. Pedal would go almost all the way to the floor before starting to engage.

Got a new (Chinese, cheap, but lifetime warranty) master, and all was good.

The other day, pedal went 1/2 way or more to the floor before engaging, but seemed to return to normal. Got home, and it was doing it again. Went out the next morning and it was 100% consistent, 1/2 way or more to the floor before starting to engage.

Went out this morning, and even worse, pedal to the floor, couldn't get it in gear, car starts moving.

Got a new master, and cannot bleed this thing. Bench bled the master to no bubbles. Put it on, and with someone pumping the pedal, went through an entire bottle of brake fluid, and every pump is the same at the slave: at least 1/2 air and half fluid.

The system is not leaking, so how can that much air continually be in the line? and why can't I clear it?