><< I have noted a variance In pedal movement that I have tracked to amount of
>vacuum in the system. >>
>
>Better stay on the trail because, considering the functioning and
>construction of a vacuum brake booster, it is impossible for a vacuum leak
>to change the
>amount of brake pedal movement.  A vacuum leak might cause the perception of
>the amount of movement to seem different, but that is all it will change.

Indeed, your point bears repeating. There is only two ways for the pedal
travel to change to any significant degree: fluid escaping from the system,
or air in the system. if there are no visible leaks anywhere and the system
has been bled of air, then the only remaining explanation is the piston
failing to pressurize the system because (as you say) fluid is leaking past
it back into the reservoir. Hydraulic brakes aren't that complicated (until
you get into anti-lock systems-- ugh), just a piston pushing fluid to other
pistons. Vacuum assist is a separate system, amplifying the pedal input.