I'm having hard time picturing (imagining) how this roller thingy can be that far off from the darkslide. On mine, it is held by a pair of black clips on both end which is screwed into the frame by tiny screws. Is your clip bent up? Is the rod bent? Does the roller actually "roll?"

That ought to be an easy fix, I think??

I'll be glad to take as many photograph of mine for comparison as you need to get you going....