Can't recommend WD-40, the solvent will clean out the lock but the lubricant doesn't last very long and then it turns to varnish. Graphite works but can be messy, personally like the liquid graphite. The graphite is suspended in a solvent, it evaporates all that is left is the graphite. Most of the time i use the teflon based lubricants, tri-flow, break-free, and several of the dry film teflon sprays. Whichever can is closest when i need it.

Since you are doing lock up duty some of the teflon sprays are available in small pocket sized applicator/spray tubes so that you can have it with you when you need it.