Ive seen reports of it drying out rubber, but in my experience I've never had a problem with overspray. There are a couple of types of plastic to avoid using it on, but rubber, seals etc. have been fine for me, but I don't dowse them in the stuff. Also, I'd doubt it does much that's useful for the rubber. A silicone based product helps bring back the flex in old rubber. Something like Gummi-pflege.