Metal Protecting !

i wouldn't use any type of grease because it could accidentally be wiped off [ without knowing it ] & rust can start. As post #19 correctly states, engine oil will eventually evaporate.
ATF is the best stuff to use. It is liquid, will 'flow', & therefore cover everything & does not evaporate. And it can be old, used ATF. I always keep a gallon of old ATF handy for rust proofing parts.