Question about Ampico valves for you player people

[PIANO2NR@AOL.COM]

I have a customer with a Haines Bros. upright with a model A Ampico with the 
valves that are "upside down".  He and a friend rebuilt the thing and did a 
reasonably good job with the following exception:  to replace the pouches 
they used zypher skin.  It is very airtight but in this configuration with 
the upside down valves it is a little too stiff and has settled and taken a 
set in the open position at rest.
     Needless to say it takes very high vacuum to close the valves now.  I 
was wondering if there is anything short of repouching that might work, such 
as treating the pouches with neatsfoot oil and perhaps using some very weak 
coil springs(like the ones at the bottom of Pianodisc solenoids) to push the 
valve disks back up to a closed position?  Any input would be appreciated.  
If you want to email me privately that's fine.
Thanks,
Randy Mangus, RPT