Door Locks Don't Work in the Cold

I have a 2004 Cavalier with manual locks. When it gets cold out the locks will not turn on the passenger or driver side. I have to go back and forth for a while before it will unlock the door which still takes a lot of force. I took the car to the dealer and they sprayed graphite in the locks and said that is all they could do because they seemed fine in their nice warm shop. This did not solve anything. I then took it upon myself to remove the door panel and try to spray all parts with WD-40 which also did not do anything. Does anyone have any ideas on why this happening or what can be done to fix it?

Thanks

Just a normal J issue. Mine did this as well when it was extremely cold. Could try picking up lock de-icer at a parts store. Best thing i can tell ya to do.

Preferably with a graphite lubricant.

I had looked at a friends car with that problem and looking a bit closer at the mechanism i found that some rustproofers just slop the stuff in without care. Remove the mechanism(not the key part, the jam part) and soak in solvent over night. Blow the part out well, gob some fresh grease in it and reinstall. Take care to mark the rods and there orientation and keep your eye on the clips.(they fly fast sometimes)Good luck !