I have found that pure silicone spray works well in restoring and preserving true rubber items, I don't like Armour all and the like as they are prone to leaving stains after repeated use especially if moisture is left on the item. Silicone also evaporates at a much slower rate the "protectorants" and as such tends to help in keeping rubber from hardening. That is good news for gum side walls which are of a higher raw rubber compound than the "black"