Use common dielectric grease (electrical-grade silicone grease). Keeps
moisture/oxygen away from the mating metal surfaces (eliminates
oxidation), and the spring pressure built into the contacts is enough to
push thru the grease for good electrical contact. The auto parts stores
have those Permatex foil envelopes at the cash registers - I think
it's labeled connector grease or electrical contact grease - something
like that.
--
Bill Putney
(To reply by e-mail, replace the last letter of the alphabet in my
address with the letter 'x')