I'm working on my 3rd set in 9&1/2 years of ownership, that is jacks and motors. I do use mine in the winter and the roads are salted so that doesn't help.
Put the camper back on the truck and then trouble shoot from there, most likely the motorhead, I think Panther RV has the best prices, I ordered 2 this spring. HJ used to sell rebuilt motors, but apparently they don't anymore since the full intregation into Lippert Industries. To tell you the truth Happijacs are pretty much junk, even their supposed new and improved models. Just my 2 Cents.
I am presently (maybe just wishing) looking at new campers and I refuse to buy any camper that uses Happijacs or is that crappijacs. That has been the number 1 constant problem with my camper. They used to have very good customer service through a guy whos name I forget (3Tons might remember), but since the full takeover by Lippert that is no-more.