Hi Everyone,  Those Lester valves can be very pesky, indeed.
The valve leather needs to be nice and smooth, and not too grainy.
The inquiry said they seemed to seat okay on a test jig so I'm
guessing the leather is not "too" grainy.

The real issue is in the wobble.  The force fit collars need to
be set on there in such a way that leaves the vacuum side of the
leather to felt washer to valve stem seal assembly with quite a bit
of flexibility.  Try looking at a Standard Pneumatic valve assembly
and duplicate that approximate amount of (for lack of a better word)
"wobble."

All player actions that use metal valve stems and force fit collars
need to have just the right amount of wobble to seat correctly.
This allows the valve leather to seat with some flexibility in the
seating angle.

Hope this helps,

Ben Gottfried - Ben's Player Piano Service
Richfield Springs, New York
http://www.bensplayerservice.com/