The best way to seal bellows that are leaking is to recover them with
new material that is airtight.  You will only make a mess that will not
last should you "paint" them with rubber cement, latex rubber or any
other material.  It is a good idea to seal the wood when you recover
bellows with shellac.  Only shellac will seal the wood airtight and
stay in place.

It is also a very good idea not to use white or yellow glues in the
restoration of your organ.  These glues are often used to hold nipples
in place and that is also a poor idea as shellac will hold the nipples
airtight.  The yellow or white glues dry and open up allowing air to
leak.  On rare occasions I will use yellow or white glue to hold some
veneer in place if you refer back to my articles on veneer gluing.

Don Teach - Shreveport Music Co.
Shreveport, Louisiana