Problem w/Monorail Movement

I've attached some pictures to show how the rear standard of my 8x10 sits on the rail. The problem is that the movement is very slippery -- with a little effort, I can push or pull the standard along the rail. When turning the knob, the internal wheel tends to slip and turn in place. You can see that the rail has three tracks -- the top two seem to guide and support the standard via the nylon guides inside the clamp. A wheel rotates along the bottom track. It could be worn, but it feels like it's out of adjustment and not making good contact with the track. Funny thing is, it works just fine on the extension rail I have -- but I'm trying to make it work on this single long rail. The first three pictures illustrate what I have.

Another question: There's an adjustable piece that fits into the bottom clamp of the rear standard. When tightened with the underside knob, it pushes two triangular stoppers up and into the bottom track of the rail. When loosened, the stoppers are gradually released from the track. Is this to lock the standard in place (i.e. lock focus)? It's confusing because the front standard has the same piece, but the stoppers have a square profile. Why should they be different? See the last picture.

The camera is branded Wonderview, an obscurity. I was told the parts resemble Plaubel, and I wonder if they're compatible.

Thanks for taking a look.

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