"Hmmm, I wonder how all those switches immersed in oil ever work ?? "

They are designed for it. Line of contact where the spring pressure rests and forces metal to metal contact. This is not the same thing. this is a round cylinder with a clamp on it that is supposed to make connection good for a couple hundred amps. When GM came out with the side post battery, there could be grease in there because they had raised parts on the connectors that actually dug into the lead. Really, side post batteries were a disaster, a piece of ****. I knew alot of people who converted them to the normal top post.

Thing is, the terminals that connect to the batter are smooth. If they put teeth on them that would be different. then you could grease the **** out of them. bnut they don't do that and actually they have good reason.

Bottom line, clean everything best you can, make the connection and tighten it, and then apply the protective grease of your choice.

Take my word for it, I have been at this for a while.