Have a look at the front of this section in Truck Campers under Truck camper University. Go way down to the section on Camper Jacks and look in there. There is complete take apart and lubricate instructions, parts lists, etc available there.
I took apart and lubed all four of my jacks in a day.. first one was 3 hours careful... by the fourth it only took an hour. I came up with a rig into my battery drill so that I could run the screw up and down with one hand as I applied grease lube to the threads.
Check it out, hope you find your answers.