VehiGAS, I did find a small leak in one of the stainless steel lines that I installed (my fault because I didn't tighten it down well enough), but the pedal drop was the same before and after fixing it.

Bart, I'm running drilled and slotted rotors by SP Performance with stock brake pads and the VX will stop on a dime and give me change if I need it to. Once I'm stopped, though, if I keep pushing on the pedal it will eventually go down to the floor. That's why I'm thinking that the seals in the master cylinder are going bad because they work initially, but the fluid must creep by them under additional pressure.