I have never had a brake system that, if air was being leaked into the system, would also not leak out brake fluid if the brake pedal was depressed vigorously (with engine running) if power brakes) several times. Pump the hell out of rhe brakes, and then religiously check every part of the brake system for visible signs of leaking.

As I noted before, if you're not leaking fluid, and you can't get adquate pedal by bleeding the system, chances are you have a bad master cylinder. If the piston(s) in the master cylinder are worn and letting fluid get past them when applying the brakes, the symptms will be exsactly as you describe.