All glass, including any type of safety glass, carries some potential of danger in handling. For safety reasons always use protective eyewear and gloves, in a well lit area when working with glass.
Removing the Existing Pane:
It is recommended that this pane be replaced with a complete new vent assembly. Automotive locks require that the glass have holes drilled through it. Most glass shops do not have this ability.
Remove the screen assembly (see appropriate section - Screen Replacement and Re-Screening). With the window closed, hook the exposed end of the two piece upper track and carefully pull it out of its groove. Work it loose and set it aside. The track is not symmetrical; note the orientation of the track in the groove. Move the opening pane to the fully open position. Hook the other top track loose and carefully pull it out. With the top tracks removed, the vent pane can then be removed by lifting the pane upward and swinging the bottom out toward you.
Replacing the Opening Pane:
Reverse the procedure above: Drop in the vent glass and slide to full open position. Install shorter track above the open area, with the "pressure leg" of the track pushing the glass outward. Slide vent fully closed. Install the other track above the stationary pane. Test for easy sliding and locking.