Laudable restoration goals should include among other things
historical accuracy and reversibility.  I've heard from many and
agree that "Best test"(tm) rubber cement with "Bestine"(tm) thinner
should be used to seal pouches.

However, never say "never do" or "always do" because there are
situations that leave no choice but to break with ideal rebuilding
goals.  Of these situations I'll mention this one, which is relevant.

I had a cross-valve Duo-Art grand that had poor repetition.  I tried
everything many of the best in the USA told me to try.  These
rebuilders also told me that certain "cross valve stacks" have
repetition problems with or without valve cap conversions.

I believe I had no other choice but to use silicone oil on the pouches.
Rubber cement gives the pouches a certain amount of stiffness which
I believed I could not afford in this instance.

Tip: try fish glue on pneumatics, it works great!

Bill Maguire