I agree with the others, you many google for days trying to find a worm gear and never get one, ordering a complete replacement is probably the best way to go. Make sure when you use the jacks that you don't crank them down too hard. They aren't meant to life the trailer.
Model X19H Expandable
GMC Sierra Pick up
Been a camper since I was a kid, and that was a long time ago :)
From pup tents with no floors, to tents with floors and flies, to a pop up, to the expandable.