Have been using the rubber cement method of sealing pouches for over
20 years and have very responsive pouches.  However, I alternately
blow and then suck on the pouches when applying the rubber cement.
You would be amazed at all the holes in some of the new leather
pouches, when you blow on them millions of bubbles appear.  When you
can blow and there are no more bubbles, it is sealed enough.  I don't
use a brush, just rub some in with my finger, you can put small dot
of masking tape on center if desired.  Johnson's baby powder is best,
seems to have some softening agent in it.

Bill & Dee Kavouras