As others have said, it's not the booster, the booster only reduces pedal effort, a dodgy one will give you a stiff pedal, it won't let the pedal drop to the floor or give you no brakes, you'll just have to push harder.
Is the fluid level going down?
If it is you should be able to see a leak.
If it's not the master is bypassing internally, probably able to kit it if the bore is ok.
Jon