I see no one has bit on this. Don't know how close my rig is to yours (WRT step cover), but I'm guessing your problem is not that of lubrication. I think perhaps that a screw (or something else) has jammed itself in the track.
So you need to be able to see what is happening underneath, but where you need to look can't be seen due to lack of step travel.
Would a small video camera allow you to "see" up under there? One of the least expensive cameras I've seen is on ebay, Item number: 260811060630. Your on-board TV can act as the monitor. Maybe this would help you discover the step obstruction. If nothing else, you get a cheap back-up camera out of the deal.
Robi & Dale ---- Go Navy ----
2016 Winnie TOUR 42'
Tow: '19 Buick Envision
or: '08 Buick Lucerne