[dsraven]

One other thing to check, maybe you have already, is to ensure the pushrod from the booster to master has a little Freeplay so the master piston is allowed to fully retract. It would mean pulling the master away from the booster enough to do the pushrod length from the master mounting surface on the booster and likewise checking the depth of the depression in the master piston where the pushrod "pushes". Then compare the two. Should be a little play there.