My old cap was doing the same thing. I replaced it with a plastic cap, a lot are using plastic now so that you can't crank it down and overtighten it. It works great.
There should be a little buildup of pressure in the resevoir of the MC in the beginning of the stroke.
What about your hand brake, perhaps that would work well enough to dump that one last load.
I went through my whole braking system, it's the only way to go.
