In 56 years of restoring automatic pianos and organs, we've naturally
run across many instruments that were previously repaired one or more
times. Instruments had the pump leather and stiffeners reglued with
every imaginable glue, including Barge's cement and other contact
cements, hot melt glue from a glue gun, PVC-E, white glue, yellow
glue, etc. In every example, the glue took much longer to remove
without damaging the underlying wood than original hot hide glue would
have been. 

I've never seen contact cement or the other modern adhesives used
by an original manufacturer. All of them used hot glue, which is easy
to remove without any damage to the wood, leaving it ready for the
new leather to be glued with hot glue again.

I've also never seen an instrument in which the original pump covering
came loose when originally glued with hot glue, unless it had been
exposed to extreme moisture conditions that caused other damage as well. 

Some hobbyists have the attitude that their work will last forever and
the pump will never again need to be recovered -- or, at least until
they don't have to take care of the instrument any more. No work lasts
forever. Please consider that some day a new owner will need to have
the pump restored again, and it will cost that owner more if
difficult-to-remove adhesives were used.

Art Reblitz
Colorado Springs, Colorado
http://www.reblitzrestorations.com/