I realize I am stepping out of my area of knowledge when it comes to
reproducing pianos.    However, when I recover player valves there is
a rule that usually works well for me:  A valve that rest against wood
is usually covered in a suede type leather; a valve that rest against
a metal seat is covered in patent leather or a smooth slick leather.

All valves have to have some play in them.  It is best to always glue
the leather to the outer perimeter of the valve and not the whole valve
surface.  This allows the valve to seat better.  Valves should travel
.035 to .040 (at least in a Seeburg).

On some outside valves that have a stem going through them with a set
collar there is no need to glue them.  Rubber cloth applied first to
wooded valves and then leather are prone to be more airtight in theory.
Now let the debates begin.

Don Teach