'88 240 DL sedan

Everytime it's dopped bellow 20 this year, my dirver's side lock has frozen. Well, the temps dropped Monday night,and when I got home Tuesday morning (around 3 a.m. I work 2nd shift) my lock was frozen. I was able to get it to unlock by pulling it up and down a few times. When I got out, I closed it but it only latched half way for some reason. Then I had trouble unlocking it because the lock cylinder was frozen. Anyway, I finally got it open, closed correctly, then I locked the door. Well, yesterday afternoon I went out to get in my car and the lock was frozen. So I climbed into the passengers side, and drove to work. When I got there, I remembered I had a little can of lock de-icer. So, I got out through the passengers door and de-iced the lock cylinder. This worked, and I was able get the lock open. Well, I thought maybe the catch was freezing too, since I had it close halfway earlier that morning. So with the door open, I sprayed some of the de-icer on the door catch. As I was doing so, I accidently flipped it up into the "locked" position! I played with it until my hands were numb,but could not figure out how to get it to release. So, I wire-tied the door shut and when to work. Then, I drove home (40 miles!) while holding the door closed!

So, how do I fix this!? I'm sure it is something simple, but I couldn't figure it out. I'm sure I'm not the first person to do this. At least I hope not!