repair – How can I seal the sticky rubber on an aging Sigma lens?

I have been gifted an old Sigma lens from around the early 90s, but as is common with the soft-touch rubberised coating on lenses of this age, the material has started to degrade and has become sticky.

As a number of plastic formulae can be carcinogenic when they break down, I’m reluctant to use the lens until I can do something about it.

I have read a lot of information on how to remove the coating, and it seems that isopropyl alcohol will do the trick, so long as it’s sufficiently pure.

I have enough 99% IPA to do the job, but this would mean removing all the lining and lettering on the barrel, which I would rather avoid.

As an alternative, I’m considering sealing the material with a transparent layer of varnish, and it has been suggested in a number of threads on various sites that polyurethane might do the job.

Although this has been suggested in many places, nobody has reported back with any detail about their success.

I’d be keen to know if anybody on here has been able to seal the rubberized coatings on a lens with polyurethane or another similar clear coating.

The lens elements themselves are intact and pristine, so I’d like to save the lens if at all possible. I’d expect that a water-based clear coat would be the best solution as anything with a harsh solvent would probably just dissolve the coating further.