The driver's side window on my 76 Aspen wagon is slightly loose. At the top of the travel, there is a lot of play forward and backward, and to roll it up all the way I have to push the window forwards and then backwards with my fingers while rolling up. I took off the door panel and took a picture of the slider assembly.

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Obviously the plastic piece on top is broken, but I don't think that's causing all the problem. There's enough space inside that plastic piece for it to shift around on the rod without even bending the plastic piece. Is something else here missing?