I didn't put any when I cleaned mine, and it works, but I can't say for how long.
If you use any, for sure dielectric. It supposedly gets scraped away when the switch moves, so doesn't interfere, but I assume that means it also doesn't do anything since it gets scraped away.
I think, leave the metal dry, and grease up any other moving parts.
1998 24V DOHC Mercury Sable, Station wagon