I had that same rust forming on mines what I did was put some black RTV gasket maker, under and above where the wires come in at the firewall, there is a indent I lifted the wire out of this indent put a glob of it in the indent pressed the wires into to then put a glob on top of the wires. For the life of me I couldn't understand why lincoln used a sponge material to seal that opening. Then I made a edging on the cover from the rear to just past half, cause my oil filler tube is leaking at the gasket where it seats in to the valve cover. tighten it down and left it, haven't been in there so I couldn't tell you if it worked but I assume it did.