I have been rebuilding the valves in one of my late Ampico model A
pianos.  The valve seats are made out of a plastic-like material which
I am told is shellac, the same material used in the manufacture of
early 78 RPM phonograph records.

The valve seats should be removed, resurfaced and replaced.  If you
are careful the valve seats can be removed, but in the process I seem
to break at least four of the approximately 83 of them.  To replace
them I used a 3D printer and printed new ones.  All I had to do was
to make a simple CAD drawing of the part and the printer produced them.
I was thinking it might be useful to keep a library of printable parts
for the mechanical music hobbyist on a web site somewhere.

Most people don't have 3D printers in their basements, even though
I think Home Depot now sells them.  Look for a "Maker Group" in or near
your community.  They are sometime called "Hacker Spaces".  They are
popping up all over the USA.  We have three in the Denver area.  The
space in Longmont where I live is called "TinkerMill".

If you don't know how to use a CAD program or operate a 3D printer,
you can probably find someone at one of these spaces who will be glad
to help you, for free.  What is a hacker space?  For some general
information go to Longmont, Colorado's TinkerMill:

  http://www.tinkermill.org/ 

Bill Decker
Longmont, Colorado