This was interesting, I have been going back and forth trying to decide on having a swiveling Driver seat and/or Passenger seat. It impacts the build design as to what is directly behind the seats but they are expensive.
So, the other day I was sitting in the passenger seat and wanted to see how much it moved forward and back. Reached down and found a lever, but it moved up and down.. I said to myself, “Self, that doesn’t make sense”
So for the first time ever I actually looked under the seat and found it was on a pedestal, not a frame, and the lever unlocked a notch.
Pulling the lever out of the notch, the seat would not rotate. Time to take the seat off the pedestal and see what is happening. OH, and yes I finally found the lever to slide the seat front to back as well.
Interesting enough, with the seat off, it is obviously a swivel.. just not working.
So I dug in a bit deeper, and it turns out [pun intended] that the two red disks act as a viscous damper while it swivels. 
Just by putting it all back together, and adjusting the lock nut, it now works.
I think I will leave the seat as it is for now, and 1st replace the driver’s seat with a new working air-suspension unit. I suspect I will not have the drivers seat swivel and build a wall behind it. The thought is to have a set of sliding doors to close off the cab securely from the cabin. And as part of that wall, build a combo closet / slide out toilet / shower affair. Still mulling on that though.
One thing I am considering on the passenger seat is making an easier way to activate the swivel, because when the seat is rotated to face the back cabin, and slid forward towards the windshield, it’s very difficult to reach the release lever. I also want to put in a few more slots to lock the seat in additional positions.
