vaseline is a dielectric.....its a very good one too...

you dont need a lot and you are not using it for its insulating
properties...you actually would be better off with some sort of
conductive grease...Ive used heat sink grease before...and it works
too.....vaseline is more likely to be around the average houshold
though...graphite would also work and its conductive so it might be a
better choice if you have some handy.

you just need a lubricant and you dont need much.