I'd recommend this spray-in stuff, "oxidation preventer", not dielectric grease.
Page 38 in this PDF, Wurth Contact OS, is the right stuff to use:
http://www.wurthusa.com/project/media/new_online_catalog_2010/04_Chemical.pdf
Nothing in the cap, that has a rubber seal and should stay dry, but some guys in the shop would spray the Contact OS in there.
Gilly