I never quite understood why these gaskets are necessary or helpful.
Original pneumatics that are glued directly are easy to remove by
cutting the cloth all the way around, bending the movable board all
the way back, then placing a hot old iron on the glued board.  When
the heat is right the boards come off easily with a putty knife, or,
in some cases, by just pulling with the finger.  An entire stack comes
apart with no damage.  Easy.  Conversely, I've seen rebuilt stacks
where gaskets were used where the pneumatics fell off prematurely.

As for re-gluing, I side with those who think anything but old hot glue
is a travesty.  I've seen too many attempts with other means -- always
a disaster.  As for proper sealing, this should not be a problem if the
surfaces are properly prepared and held together with adequate force.

The occasional leaker can be sealed during the test for air-tightness.
With the re-glued, rebuilt pneumatic in the closed position, block the
air supply and try to pull the pneumatic open.  You'll know if there's
a leak that needs sealing.

Craig Roothoff
Escondido, Calif.