Yesterday when it rained and snowed and then froze, I could not unlock my driver's side door with the key. The key wouldn't go all the way in (if you know what i mean)...

I wound up unlocking the doors from the passenger door lock, then crossed my fingers and gave the driver's door handle a tug. It worked. Once i warmed the car up, i could unlock/lock the driver's door.

SO. my question is, 1. how can i prevent this in the future? 2. I'm tempted to spray graphite into the lock, but don't want to cause more problems till i get your guys feedback.

Thanks in advance.