maybe it's binding a bit on the floor hole? I've had one do that - they get pushed sideways sometime w/ age because no one ever pushes straight down
if it is the pivot on the master cyl, it could be the pin worn, or the eye on the plunger is a bit oval from years of not being greased, so you'd have to take it apart and see - don't know of anyplace those bits can be found except good used, or you could clean it up w/ some weld and reshapeing
Bill
