Cutlass Supreme S 1992 - Frozen door locks

Hi there,
I drive a 1992 Cutlass Supreme with the door knobs that go up and down. Last winter I had a heck of a time with the door locks freezing. Actualy there were two major problems. 1) the lock would
freeze 2) Most of the time when they did open or I finally got them open the latch that keps the door closed would stay stuck in the open position. I would have to tie a bungee cord from door to door to keep it shut until the car warmed up enough and the latch would release and lock. I put so many different types of lubricant and lock de-icer/anti-icers on the lock, come spring the locks were damaged and I had to replace them.
I really do not want to go through this again this year. Does anyone have any suggetions? (Other than getting rid of the car)

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