Help! One of my jacks won't retract or extend!

I only load and unload about once a year. As I understand it lack of use is hard on the jacks. I have also never tried to lube them. Last year trying to load for a trip, I also had one jack fail. I ordered two jacks. They arrived within a couple of days. Replacing the broken jack took only a half hour or so. I now have a spare just in case.

BTW, you should have no problem using the 3 good jacks to raise the camper and allow you to replace the broken jack. Just don't wait until you have two fail.