"BeeJ" wrote in message
...

We need more information. (I have no idea what you mean by
"used for light blocking like on a camera lens".)
There are rubber rejuvenators, such as Fedron. Are they what
you're thinking of?

MSDS shows it is mostly a cleaner. I do not need a cleaner.
I need to protect from UV and air impurities that will deteriorate
the rubber.

Regardless of the what the MSDS shows, Fedron works as a rejuvenator. It can
soften badly hardened rubber.

Do you know how to use a search engine?