I have repaired three of these machines over the years.  The main
problem I found in all three machines is "Perflex pouches" in
everything!  The stack, the play/rewind/cointrip valves, all of the
percussions and bells have Perflex pouches.

The only way to repair these machines is to replace all of the pouches
with leather (like they _should_ have used).  The percussions are
fairly easy to repair, due to the fact that they easy to remove from
the piano and repair.  The bells also need pouch replacement as well.

The fun part is removing the stack from under the keybed, disconnecting
all of the hoses, and keeping track of which one went where.  I taped
a piece of paper to the underside of the keybed, drew a layout of the
tubing coming down through the keybed, then drew lines from the tubing
to the stack and the valves below.

Once you get the stack out and apart, carefully pry the plastic rings
out of the pouch board, then glue leather pouches to the bottom of the
rings, then press the rings back into the pouch board.  To get the hang
of replacing the pouches, start with the drums (the snare drum is easy
to remove).  This is a valve that connects to the bass drum center
beater (the big one) and the ride cymbal.  Don't forget that one.

Have fun!
Mike