Power Booster or Master Cylinder

I have a 1998 Taurus with out ABS.
When I apply the brakes it feels spongy then will hit some resistance then slowly drift down a bit then hold. If I creep forward letting foot off brake and stop again the pedal travels farther toward floor, repeat 3 or 4 times and I'll have no brakes.
Pumping brakes will get me to be able to stop again.

I have bled the brakes, car has no oil or vacuum leaks and the booster check valve is functioning properly.

I assume this is the Power Booster or Master Cylinder but I don't know which.
Your help would be greatly appreciated
Bruce

Sounds like the brake master.

Agree with KimMG. If it was the booster, the brake pedal would be real high and real hard.