I have seen some sliders so jammed up with crud that no soaking freed them.
But you might want to remove the slider from the ladder before taking it apart.
That will give you more access and more play to try to clean it further more, before attempting disassembly.
There is an armorer tool other than the combination tool that was issued to individual soldiers.
I have one i purchased some time ago.
You should be able to make one with a screwdriver.
It's pretty simple, but effective.
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