Hi Peter,  For really quick repairs I use Contact Cement and medium
weight (0.020") Cabretta.  But don't just patch the holes.

Surprising as it might sound, I've discovered that a significant amount
of leakage occurs near the top of the bellow, especially when 'modern
day' cloth was used to do the previous rebuilding.  Also, a thin strip
should be applied to the 'fold' up the sides.

If you have the time and the supplies, I've also had a lot of luck
sealing reservoirs with Phenoseal in areas that are not under as much
stress as the folds.

These are ONLY temporary repairs, but they do work.

Musically,
John A. Tuttle