In the last few campsites one of the levelers refused to retract. To get it up I had to drive forward enough so it could swing up. (Yes, the levelers are designed for that). The shiney piston part simply would not retract all the way in spite of pushing or banging on the base. If there was clearance it would extend properly for leveling but not fully retract when done.
A search came up with the suggestion to fully extend the jack, spray WD40 generously inside the metal sleeve at the top of the piston and ,using a twig or stick, swab a paper towel around inside the metal sleeve. I did that repeatedly until the black gunk up in there was gone. That was followed by spraying WD40 all over the piston and wiping it clean of any residue.
The jack retracted normally after this treatment and has been behaving properly since.