I recently posted this on another forum but may be pertinent to repeat here. I'm looking at a bottle of "Rubber Renue" which is made by M. G. Chemicals Ltd in Burlington, Ontario, Canada. Web address is www.mgchemicals.com
. The bottle lists ingredients in the following order: xylene, acetone, methyl salicylate. I've yet to try Rubber Renue on any stylus, so have no experience to relate.
Re the original question, Shure has stated somewhere that it's ozone in the atmosphere which degrades stylus suspensions. So perhaps degradation depends on environment. I keep my spare Shure VN5MR styli in an airtight container.
The only Shure stylus suspension that has gone sour on me was for a V15 Type IV: that one has a two-part rubber suspension/vibration absorber construction quite different from other Shures.
I have some much older ADC styli that appear undegraded after many decades.