Jack

I like the bypass the booster idea. They are VERY often problematic and if they can't maintain vacuum they just might cause the issues you are seeing. My wagon stops just fine without one and it is a pre-disc brake model!

Another thing I would check is for deterioration in your flexible brake lines. They can deteriorate internally causing the inside to swell "shut" or at least constrict the inner passage to the point that they won't allow pressure to be transmitted.

My pressure bleeder cap would pop off too, so I wrapped a double layer of paper towel around the lip and it helps to keep it form slipping off under pressure (plastic agin' plastic lubed with brake fluid is real slippery and the paper towel adds just a bit of friction between the two).

Mike