The HD floppy in my A4000D has recently picked up the bad habit of sporadically "greeting" a disk, when no disk is present. To mitigate, I can grab the sensor arm with needle-nose pliers and manipulate it a bit. Then the drive behaves until the next disk is inserted and removed, then it starts again.
So it seems the lubricating the arm which extends out of the switch would fix the issue, but I am leery of using something like WD-40. What would make a proper lube for this: mineral oil, WD-40, electric motor (or machine) oil, or what?