I always wince when I hear people - and usually people who know much, much more about cars than me - recommending vaseline for rubber parts. Petroleum products should never be used on rubber, it breaks it down. Silicone isn't fantastic either. With rubber, if you're not sure the best thing is just to leave it alone.
I have a whole lot of stuff to fix on my car over the weekend & coming week.. two outer CV boots, a steering rack boot, an exhaust leak and a drive belt. The car's only done 67,000 (kms, not miles) but it's an '86 so I guess some parts are going to deteriorate even if it had been sitting garaged the whole time. I can't afford to get anyone to do it, so I guess I'm going to have to learn