I'm still betting on the guide part...it allows the rail to pivot appropriately are the window travels to the top.

Forgive me as I hadn't done this since 2001, so I can't remember the condition of my guide piece when I looked at it.

But when it fails, the rail gets hung up near the end of the upward trip (as you have witnessed).

Certainly the cheap route to go even if incorrect, but I'm 99.9999% sure that's the issue...

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