Don't use Vaseline, use dielectric grease (typically used for spark plug boots) instead, it's made for electrical applications.
And don't mess with the foam ring thing, that's just asking for trouble. If anything, get a nice tube of RTV silicone and apply a modest amount to the area. I'd almost suggest some of that self-curing/expanding foam (
http://www.dow.com/greatstuff/) but that's gonna be a bitch to remove if/when you actually need to get at anything under there again.
Brent