Mushy brakes

[YankeeClipper]

My IA, who has been working with at least two other skymasters, has been struggling with my brakes. Every time he tries to bleed them he struggles to get good pressure at the pedals. The Masters have had all replacement parts replaced, the swivels have been rebuilt, and no fluid is leaking out anywhere. Has anybody run into this, or does anybody know of a secret to refilling and bleeding the brake system? I think all units are the same, but mine is a delta model if it matters.