I have a '96 Ford Escort and any time the temps get below freezing, the lock on the driver's side door won't unlock with the key. I can unlock from inside and then it will work, under protest, with the key. Does that stuff you spray inside the lock really work or do I just need to get the lock replaced? This has been going on for some time, but seems to be getting worse. I have sprayed graphite in the lock a time or two, but that's all I've tried. Have heard not to spray any type of oil in there (WD-40, mineral oil preparations, etc.), so hesitant to use anything like that. Suggestions? Comments? Thanks!