As an experiment on an automated player bellows while I was doing a
favor for a volunteer museum (translated: lots of work and no cash!),
I used some of that spray rubber sealer you see advertised on TV.
The player bellows was intact, but the rubber was cracking and leaking
badly.

I tried the spray sealer, used two coats, and in an hour and a half the
piano was playable and had great vacuum.  This is not a substitute for
a real rebuild, but worked fine and it is still holding months later.
I'm curious to see how long it holds, but it has good results so far.

Bob Noble - Noble Piano Services
Mansfield, Ohio