As a teen (long ago!) I worked for Johnny Green around l960 who rebuilt
players from the l950's to the l980's.

He had a piece of pipe about 3" in diameter, threaded at each end and
capped.  He filled it with gasoline, put the tracker bar in overnight,
and voila!  In the morning out came the tracker bar with all the rubber
softened, and it just about fell off the nipples.  A clean and simple
job.   (Just don't light your cigar!)

Marc Goodman
Cleveland, Ohio