AuroraGirl
I'm Awesome
nothing a little mapp gas torch couldnt fix or alleviate frustrations(but possibly not fix the problem)that's exactly the only thing that should be used as a lubricant inside locks. graphite lock lubricant.
Also I have a few of those lock de-icer bottles as some of my outbuilding get water or snow blown in that then melts and freezes.... I learned a long time ago that if you need the de-icer and its behind the lock, your screwed! I keep these little bottles in the fridge where I keep my gas tanks. unlocked and accessible.
Lol, kidding.
I would personally, if possible, spend the time to bring the vehicle in to something above freezing, get it warmed up. Shoot air in it, also have a vacuum, work the lock while doing this. May need helper. get it cleared out(could also remove from door but thats more work) maybe try a evaporating solvent if you know what you are doing and smarter than me on this stuff, get it clean. then use a PTFE lubricant . Graphite could be used, but if your lock is apt to take on water, sap, or someone spraying something into it, I would use teflon instead.