Not all windows have a rivet or stop screw in that upper track. Easy to remove the Phillips screw or drill out the rivet. My galley window would slide aft by vibration. I utilized that feature when I'd locked the keys inside.
To get the wheels back in you need to slide one half enough to get the wheel aligned with the track and re- insert. Repeat on the other side. There is a brown plastic piece in the track that acts to stop the arms from extending. You can get the windows to open further by cutting this piece. I'm unable to find the thread where it's discussed but I think I cut mine to 6". Slide it back in and reslide the window half.
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