Pete,  I would suggest (quite strongly) that you use the hot hide glue
for your reservoirs.  I would even suggest that someone in the future
(distant, let us hope!) will curse your Titebond glue on those organ
pieces when he/she has to recover them (due, one hopes, only because
of the failure of the leather).

I just completed the re-recovering of a set of Manualo reservoirs due
to the failure of the hinges (because of an apparent "shortcut" by the
previous rebuilder), and I am _still_ cursing the (what appears to have
been) Titebond glue.  The rest of the work was beautifully executed,
save for the lack of re-hinging the main pumping bellows.  Oh, by the
way, the previous work was about 20 years old, so it did hold up for
quite a while.  Of course, this is just this one man's opinion!

Have fun!
David Dewey