specifically what rubber parts are your referring to?
FYI:
From the WD40 Website:
What surfaces or materials are OK to use WD-40 on?
"WD-40 can be used on just about everything. It is safe for metal, rubber, wood and plastic. WD-40 can be applied to painted metal surfaces without harming the paint. Polycarbonate and clear polystyrene plastic are among the few surfaces on which to avoid using a petroleum-based product like WD-40."
Even though it it safe for most anything, i usually spray On the rag then wipe to avoid getting in my bushings and other crevices that it could build up where i dont want
To someone like myself who for more than 25 years has been doing design work in the chemical industry, the term "rubber" is so generic it is never used in business.
WHAT KIND OF RUBBER???
Hahaha, yeah, just avoid that response and say what you mean around the plant.
But the company that makes WD40 gives a consumer reply of "It's OK folks!" I'm smarter than that.
Soooooooo, WD40 is 50% mineral spirits. Neoprene and EP compounds are very common for hoses, belts, weather stripping etc.
Neoprene gets a fair rating with mineral spirits, EP a severe rating for corrosion attack. Makes it look purdy because you're taking the top layer off and soaking the oily solvent into the polymer!
I wouldn't use WD40 around rubber. You can check the chemical compatibility I quote at Cole Parmer dot com's web site.