I have to comment on a posting yesterday about sealing leather pouches.
If your pouches are bad enough that you can hear hissing leaks, or see
a hole visibly, then a sealant is not the solution.  Replace the pouch
-- it has a hole in it!

Sealing a pouch will help with microscopic, otherwise undetectable leaks
and improve the performance of the instrument, hopefully increase the
longevity and reliability.  Patching a hole may be a temporary stop-gap,
but the solution should be repair and/or replace bad materials.

Eli Shahar