That is not a bad price you are asking [$500].  I was a dealer for
these pianos in those days, and that one cost me approximately
$1000 wholesale.

I am wondering if replacement valves are available.  The original
valves were made of plastic and would be tough to repair, although
I can conceive of a way they could probably be repaired if necessary:
saw them apart and after repair glue them back together.  The saw cut
material could be replaced with a gasket  of about the right thickness.

Ellsworth Johnson
Spokane, Washington