There is a thread on taking apart the jacks. It is helpful as you need to fab a little hook to disassemble and it's super easy with the instructions.
Just because you see grease on top on the gears means nothing. That's not where they corrode first. it's the big screw in the leg that gets crusty first in my experience.
The ratcheting could be due to the above, or if only 1 front jack ratcheting, on mine, the camper is a bit twisted and actually overloading 1 jack. Some adjustment in height between the jacks gets everything working again.
Hope this helps.