Rat repair.

[beardface]

I didn't quite follow your brake bleeding procedure there, but i've heard of air leaking through the bleeder screw threads while trying to use a vacuum. My dad puts a dab of grease on the bleed screw threads when he uses a vacuum to bleed brakes, and the grease seals the treads. If that sounds like your problem that could be worth a shot before you tear into your pump.
Good luck.