"To seal or not to seal?"  I must admit I've never heard that as
a question.  First of all, however, I want to agree with a previous
posting that if you have old pouches and wish to renew them, then
sealing is not an option; remove the pouches and replace them with
new leather.

That much I agreed with.  If I understood correctly, then he went on
to say "do not seal new leather," too.  To me this is not the correct
way to do things and I believe that pouches should be sealed [using]
egg whites, thinned rubber cement, Dow Corning 111 or another silicone,
or Hydrophane.  To me, it's not important which technique you use but
that you should definitely seal them.

If you take a valve without a bleed and operate it, that valve should
theoretically never return.  Try it with an unsealed pouch, then try
it with a sealed pouch.  After sealing my pouches, they would stay
activated at an average of around 7-8 seconds for me, and I had several
that never deactivate.

This is the importance of sealing pouches.  If you don't seal them,
you can have notes that release prematurely [because] the pouches leak
to the vacuum.  The ultimate of this is if you have notes that try to
flutter with chain perforations -- it doesn't mean that the note is
"tight", it means that the pouch isn't sealed.

Eli Shahar
Sonora, California