Brake Issues with the 201

[Suped.]

Did some brake work on girlfriend's '84 190e today. Sad part is, the brakes aren't any better, just different. Since we've had it, the car has suffered from a stiff pedal with too little travel. Today I rebuilt the front calipers (one was just about frozen) and we're suffering from a low, squishy pedal. The pedal is high and stiff with the car off, and sinks when the car is on. Maybe something to do with the booster? I know the booster is doing something, since the car is incredibly hard to stop with the booster disconnected.
I've bled the brakes a couple times already (and I'll be the first to admit that I'm not great at bleeding brakes). There doesn't seem to be any sign of a leak, the pedal holds steady and doesn't sink down. That seems to rule out a bad master cylinder too, which my buddy swears is the issue. Everything seems to point to more air in the system, though I don't seem to be getting it when bleeding. I'm lost, and all I can think of is to bleed and bleed until the brakes work as they should.


Two points that may be of interest:

With hard braking, the car pulls left some.

I believe the fluid was overheated yesterday. I'm wondering if there's still some burnt up fluid in the system disturbing the whole affair.

I'm open to any suggestions.