Roy, my curiosity got the best of me so I took off the end of my LS 25 to see how it was assembled. I hope these images are useful to you or anyone considering modifying the positioner.
This is the end plate. The black screw accepts a 1/8-inch hex key and uses a metric nut to lock it in place. It's function will be clear later, but it is used to preload the ball bearing that contacts the end of the lead screw.
There are five 10-32 x 1-inch self-tapping machine screws holding the steel plate to the aluminum extrusion (four of the five screws shown).
Here is an image of the steel plate and the screw.
After removing the steel plate, I can see the black ring is just a spacer containing what appears to be white lithium grease and a steel ball bearing.
When I removed the black spacer, the ball bearing is now visible.
I didn't have any grease to apply, so I didn't clean up the end of the lead screw; however, I probed it and couldn't feel a dimple, so I assume the end of the lead screw is flat.
I think you are correct about the grub screw in the adjustment knob. I didn't take an image of it, but there is what appears to be an identical black spacer between the lead screw and the front plate. I don't recall seeing an adjustment on the front plate, but didn't want to take my positioner apart any further to check.
The red adjustment knob's only function is to turn the lead screw in place. The black dial is a friction fit to the adjustment knob and rotates to allow the operator to set a new "zero" adjustment. The click stops for the increments are created by a spring-loaded bearing in the extrusion that contacts dimples in one face of the red adjustment knob.