Michael Pawelek (MMD 030615) wrote, "... Is there any chemical that
can be applied to the outside of bellows material to keep it soft and
supple without damage to the material?"
Quick answer: Apply Carter's Rubber Cement, then dust with talc.
But I am unclear why one would choose to compromise the quality and
longevity of an instrument invested with so much resources of time and
money. Your good work will not receive the same respect if you take
such a shortcut. There are already too many instruments out there with
rubber caulk, duct tape, etc.
I recommend rebuilding the bellows. The task and the results can be
enormously satisfying. These being the lungs of the instrument,
anything less will compromise its playing, mechanically and musically.