In article , mike wrote:

maybe an O-ring?
There's stuff we used to put on record player turntable belts
to stop slipping. Dunno what's in it.

The stuff I've used is "Rubber Renue", currently sold by MG
Chemicals. It contains methyl salicylate (wintergreen oil) in a
solvent base of xylene and ethylbenzene and (in one varient) acetone.
Use with plenty and plenty of ventilation!

TechSpray is selling a "greener" product for the same purpose, which
uses d-limonene (from citrus fruit peel) and some chlorinated
paraffin.

Ideally, such a material will de-glaze the belt surface (allowing it
to "grab" once again) without attacking the rubber.

Don't apply them "in place" - remove the belt, wipe on the
rejuvinator, let it sit for a few seconds, wipe off (and expect a lot
of black gunk to come off with it, as it removes the deteriorated
rubber from the surface of the belt).