Hello -- Long ago, as a teen, I worked for a wonderful player piano
restorer, Johnny Green.  He had been rebuilding and restoring players,
reproducers and nickelodeons from the l950s-l980s.  He had an easy
method of removing old rubber from tracker bars.

He took a piece of iron pipe, about 3" in diameter, threaded at both
ends and fitted with metal screw on caps.  The pipe was filled with
gasoline, the tracker bar dropped in, the ends capped and left to sit
overnight.  The next day the tracker bar was removed and the now _very_
soft rubber was easily removed!

Best, Marc Goodman, Cleveland, Ohio