We have been very successful with cleaning piano action parts using a
glass bead blasting system.  We use a very small glass bead.  With
proper control of air pressure and distance to target we can clean and
reactivate damper felts or remove rust and corrosion, and even old
plating.  All parts of the piano action can be cleaned with this
method.

What you need to perform this task is a bead blasting booth at least
as wide as your widest piano action.  The booth can be made of wood,
cloth, or metal.  Ours is of cloth (sail cloth or light canvas) with
sleeves for arms, Velcro'd access panels, and a funnel bottom.  There
are two vinyl windows to see what is being done.

We put a 4-foot fluorescent light fixture inside in the top for
illumination.  This cover is mounted over a metal frame which can be
attached to the wall of the shop when needed.  Others have made wooden
units which can be rolled around.  If you want to make your action
parts look nice, this is the way to go.  A warning!  The glass beads
are like little ball bearings when spilled on the floor.  All parts
cleaning should be done before rebushing,  repinning or replating.

Bob Lemon
Lemon's Player Piano Service
Sacramento, CA