I have used a silicone lubricant for such things, Dow Corning Vacuum Grease, which is intended to lubricate fritted glass-to-glass rotating seals such as stop-cocks. A metal-to-metal contact pushes the lubricant aside and the lubricant seals out the entry of air. I have also used petroleum jelly (Vaseline) for the same purpose, but it melts at a low temperature and is somewhat messy. If you can find it, distributor cam lubricant might be an inexpensive alternative. Whatever you use, a very thin film is all you need.