John,  Just play the piano without the end treble damper.  You won't
miss it.  If the screw cannot be removed with an 'easy-out', then
perhaps try a broken screw extractor.  This is a hollow tube which is
serrated at the tip.  This bores down around the screw until it is
loose; then plug the hole and re-drill.  Or use a narrower screw
elsewhere on the flange.

But you could do without the end treble damper.  The treble hammer
felt can be glued back on.  I use thick CA glue.  The hammer has lost
it's power but here again, you may not notice it.  Chances for wire
breaking during tuning are high.

Jon Page
Harwich Port, Cape Cod, Mass. (jpage@capecod.net)