Hi,  Thanks for the replies; some very good insight and appreciated.
I will use pouch leather as gaskets and I'm glad Aeolian did.

I would like to take issue with one thing: the claim that they would
not add the added expense only to make it possible to repair in the
future.

Case in point one: The Aeolian Orchestrelle.  The bellows of the
Orchestrelle have a special panel screwed on to them with no other
purpose than to make the internal flap valves accessible.

By the 1920s, when these were made (My Duo-Art has 9/26 written in
pencil on the inside of the vacuum chamber; I assume that it's the
date), there was certainly enough knowledge about repairs needed to
automatic musical instruments and their components.  Aeolian was making
a quality product that cost in some cases as much as a working class
home.  I do not believe that they would want word to get out that their
machine was difficult to repair.  I would believe that they planned to
be around to make the repairs themselves in many instances so it does
make sense that they would be concerned with this.

Compare this to the Gulbransen (no flames, please!).  The Gulbransen
player is one of the most difficult to repair.  There are experts that
proclaim it as a  wonderful piano, and the ability to play one fully
restored is an experience, but the rumor goes today that the stack was
meant to be thrown away and replaced.  I tried unsuccessfully to tackle
a Gulbransen as my second player.  I never got a note out of it.  That
was in the 70s, I was young and didn't have any guidance in what to do
and how, but comparing it to others that I've worked on and restored
since then-that piano was a nightmare.

Pouch leather (or any other "gasket") glued between the pneumatic and
the deck holds no real purpose for anything but restoration.

That said, I can publicly state that the condition of my piano is
better and it will withstand future restorations better because of that
pouch leather.  I only hope that the next time that it is restored the
next guy will bless me for my materials and techniques as much as I am
blessing the fact that no-one touched it since Aeolian did.

Eli Shahar