Having just returned from Bude Jazz Festival I notice the item on
pneumatic gaskets. I have come across these, and as I recall the
material used was some form of cheesecloth. The glued boards came off
very easily with no damage to either surface.  As far as longevity of
seal is concerned, I think that it is fair to say that it is probably
no less than the useful life of the pneumatic's cloth. The biggest
danger to weakening them is perhaps clumsy removal of the upper action
from the piano.  I have seen individual pneumatics that were gasketed
wrenched off due to fouling on the whippen.

Roger Waring