My wife and I have both noticed that the drivers door lock is sometimes hard to get the key into, it seems to be sticking part-way in (although it just turns just fine), and I get the feeling that it's possibly time to replace it.

Seeing as how the ignition tumbler is bound to have seen just as much use as that lock, and how I have to go to the dealership to get the door lock anyhow, should I go ahead an order an ignition tumbler as a preventative measure?

Maybe I'm completley wrong, and I just need a judicious applcation of some suitable lock lubricant, not WD40, I'm guessing - Molybdenum disulphite, perhaps?