Hi All,  I'm curious to know how Doug determined that the inside flap
valves are leaking.  First off, such leakage is quite uncommon.  In
fact, it's more common that the wood itself is leaking rather than the
inside flap valves.  And before going any further, according to the
Gulbransen Service Manual the inside flap valves are located inside
of the exhauster bellows.  So, it's impossible to access them without
opening the exhauster bellows.

A common problem with the Gulbransen Exhauster Assembly is leakage at
all of the points where two pieces of wood come together (the joints
and the seals).  Being what I call a 'high vacuum-low volume' assembly,
small leaks can cause big problems.  Because of its construction, it's
one of the few lower sections that can hold a vacuum for over a minute
when properly rebuilt.

My suggestion is to look for and repair/seal all of the joints in the
assembly before tearing the unit down.

Lastly, you can purchase the Gulbransen Service Manual online at
  https://www.buysecure.com/playercare/reprints.html#gulbransen

Musically,

John A. Tuttle