I am fairly new to player piano work (53 years as of March 1st,
2009).  I have to agree with Robert Loeffler on sealing valve pouches.
I class this with using old Model T car topping on leaky bellows.

I am now doing a Steinway Duo-Art grand (of which I have done
several, along with Welte and Ampico).  Before leaving for the
Kennewick Band Organ Rally, I helped my employee pull several of
the parts off.  We cleaned all of the pouches and I gave them the
suction test.  They worked fine so I told him go ahead and recover
the pneumatics.

Yesterday I looked at one of the pouch blocks and pressed on the
pouch it looked fine and tested fine.  I then went to re-seat it
and it virtually disintegrated.  Now we have to disassemble all of
those he repaired to replace the pouches.  We take pride in our
quality craftsmanship.  In my humble opinion I was stupid.

If a piano comes from a wetter climate to a drier climate then
definitely replace pouches and many times valve faces.  It will save
a lot of grief.

Dell Urry - Antique Restorations