Classic/Antique Car Repair: rubber parts, napa store, petroleum jelly

Question
is it ok to coat rubber parts such as grommets,
with petroleum jelly to preserve them or will petroleum dry out the rubber? i have been told
yes and no, if not what would be good to use
to make rubber soft and pliable?  

Answer
This is a question for a chemist, but I can tell you my experience - I use Silicon Grease - available at most auto parts places - as it is designed for this purpose.

It is a clear grease in a tube, with a consistency similar to that of Vaseline, but without any petroleum content, so it will not attack the rubber or any plastic you put it on - it is totally inert in that respect.

It is used in space instruments for this exact reason (my former career) and I've always used it on my cars - it keeps the weatherstrip and rubber bumpers under the hood etc. just like new - I put it on in a thin coat with my fingers, rub it in a bit, and then wipe off any excess that might come in contact with someone's clothing.

GE makes it, and so does Dow-Corning.  The DC part number is DC-4.  I got my last tube from the NAPA store - it was the GE brand, but it is just the same to use and the way it works.

Dick.