Here's how I would probably do it:
Take the trailer off the truck and support it with the legs, just like you're were camping. Then I would remove the generator and housing if that is the plan.
With the generator out of the way I would put the trailer back on the truck and locate the issues with the leg/s.
Once I found the problem, I would take the trailer back off the truck and locate the necessary parts to fix the problem. Once I have the parts I would put the trailer back on the truck, if necessary, and fix the legs.
After going through this I would change out the legs with a good after market set. My choice is Bulldog, but that's just me. This doesn't sound like something you'd want to do more than once.
Just as an aside, when I did mine I did one leg at a time and supported the 5th wheel with one leg and a tall jack that I have. Then switched and did the other leg. Worked just fine. Done in an afternoon.
