Taurus 2001 SE doors not locking in winter

Last winter I had a very annoying problem with my front doors (on Taurus 2001 SE). In the morning and after work in the evening when the car was cold, my driver door would not lock (and hence I could not drive) until the car would warm up, or until I would work out the lock by randomly pushing the latch up-and-down-back-and-forth-left-and-right for some time. I can guess that there must be a problem with the lubrication of some parts of the locking mechanism, but I don't know where and what. I would appreciate any advice concerning this problem.

I suspect that sometime in your cars past history someone has used both graphite and oil to lubricate the lock mechanism. This can gum up on a cold day. Get a can of WD-40 (I'll bet you already have one) and spray into the key opening with the include plastic straw. Then work the mechanism as you have before to loosen it up. ~Dave~

I suspect that sometime in your cars past history someone has used both graphite and oil to lubricate the lock mechanism. This can gum up on a cold day. Get a can of WD-40 (I'll bet you already have one) and spray into the key opening with the include plastic straw. Then work the mechanism as you have before to loosen it up. ~Dave~

Thanks for the advice. What would you recommend WD-40, or PB Blaster or Liquid Wrench? I have heard different opinions about them, most people say that PB Blaster works for longer periods of time, but I am not sure it is appropriate for the door looks... If I use WD-40, will it not gum again, because the old gum (i.e., the mixture of graphite and oil, as you suggested) is still there ?