I have used Dow 111 to seal all the pouches in all the single
valve players that I have rebuilt and I have had no problems at
all.  Dow 111 is not a substitute for careful selection of leather.
It will not fill pinholes or leather that has other problems.  It
will seal the pores of good quality leather and very little is needed
because it is extremely long lasting and will not evaporate or migrate.

This is the same grease that is used to seal glass joints in critical
laboratory equipment used under high vacuum.  It doesn't move.  If
you slop it all over the place it may prevent future gluing but it
will not move out of the pouch if that is where you put it.

Dow 111 has so many other uses, everyone should have a tube of it.
It resists high temperatures, water and steam and stays where it is
put.  It is the perfect grease for o-rings and seals.  A light wipe
will keep your espresso machine group (gruppo) seals in good shape
for a year whereas any other grease will fail in a month.

So buy a tube and test it on some pouches.

Best regards,
Spencer Chase

 [ Found at http://www.dowcorning.com/content/news/iam_news32.asp --
 [ "Dow Corning 111 Valve Lubricant and Sealant is a heavy-consistency
 [ dimethyl silicone compound that resists a variety of organic and
 [ inorganic chemicals."  -- Robbie