I have an exterior door with a keyhole-in-knob deadlatch. With the
recent cold weather, the latch started sticking open when it gets
pushed in while closing the door, so the door doesn't latch shut. I
figured out that the deadlatch was sticking to the main latch, so the
main latch couldn't spring back out into the door frame.

So I rubbed a pencil (a quick source of graphite) in the groove in the
main latch which the deadlatch rubs against. It worked for about a
week and a half, and now the problem is back.

Should I try more graphite, or a different type? Will adding WD-40
after graphite gum up the works? I'd really prefer not to replace the
whole doorknob lock because of this simple problem.

Jimmy