Hello again,

Scenario:  Brakes are generally spongy on first push, but catch very well after
initial pump.  Bleeding does not seem to help.  Once the brakes catch, they
only hold well for about 10 seconds, then the brake pedal rapidly sinks to the
floor.  This is bad in flat country, but really sucks when you have to stop and
wait on a hill.  No external leaks are visible, and no fluid loss is evident.

I believe the master cylinder is leaking internally, but I seek your wisdom to
verify the cause, and input regarding rebuilding vs. replacing.  Are any
special tools required for this, or should I just take it to Midas and let them
deal with it?

Thanks again,
Vernon Craddock
'90 Vanagon