tl dr - Have no fear of Vaseline and o-rings
O-rings are made out of many different materials. I would suggest that those o-rings which are made to work in the automotive realm are made to be resistant to things such as oil, gasoline, and other petroleum products. This would include Vaseline. While Vaseline and other petroleum products may degrade real rubber (actually made from the rubber tree), current o-rings technology does not use natural rubber. The Parker O-ring Handbook states:
A polymer is the “result of a chemical linking of molecules into a long chain-like structure.” Both plastics and elastomers are classifi ed as polymers. In this handbook, polymer generally refers to a basic class of elastomer, members
of which have similar chemical and physical properties. O-rings are made from many polymers, but a few polymers account for the majority of O-rings produced, namely Nitrile, EPDM and Neoprene.
Looking further into the handbook will give you this matrix of how well different types of materials fair against different things:
Looking throughout the matrix you can see that natural rubber does very poorly against oil, while Neoprene does fair to good and Nitrile does excellent. (Note: Even though EPDM is said to be used as one of the big three substances, I'm not finding it on the list.)
With this in mind, you should have no worries about whether to utilize Vaseline on any of the o-rings. Vaseline is a very mild petroleum product. If it wasn't, we wouldn't use it in so many products which involve skin care. If o-rings were actually made of rubber, then there would be concern.