These little black plastic guide pieces live at each end of the aluminum track piece that is attached to the sliding glass part of your middle side window. If you are replacing the “furry” weather-stripping between the panes, you will need to remove these, and —we’re just being honest here—they will most likely break. Now that they are available again, you can yank ’em without fear. Aftermarket item.
Two required per window. 4 total per vehicle. Fits 1980-1991.