I own a Ford Escort 1992, 1.9l, manual. Recently my default-idle had been really high and so I did some research and figured out that my brake booster probably broke. So I went to the junkyard and got a brake booster from a 93 Ford and replaced it. So far so good. The brake booster seems to work, however, I have to push the brake pedal almost until the bottom until the car is slowing down. Furthermore, recently (and this had happened with the old brake booster too at the very end) - brake fluid leaked INTO the car on the driver's side. It comes out of the clutch-pedal. Therefore, I was wondering whether both of these problems are connected? Is it possible that there is just not enough pressure in the brake-lines? I did bleed the brakes after changing the brake booster - but did not bench bleed the brake master cylinder.
Did you change out the master cylinder along with the brake booster when you did the swap? If so, you needed to bleed the brakes when you did this (assuming this from your comment about not bench bleeding the master cylinder). This would be why you are having to press the brakes nearly to the floor to get the car to stop. If you did bleed the brakes, perhaps you didn't do it correctly or completely.
As far as leaking into the car, this could be caused from a bad master cylinder. The one you purchased from the wrecking yard may just have been bad. The leak could be occurring from the rear seal in the master or from the reservoir (seal at the master or cracked). Most wrecking yards today will give you an exchange on parts you purchase from their yard if it's bad. Check where you bought it from to see.
Having a manual shift transmission, does it have a hydraulic actuated clutch? If so, this could be what is actually leaking and not the brake master. They both work almost identical and use the same fluid to actuate. Check your fluid level in the clutch reservoir to see if it is topped off.