WARNING: This page is about a different car, the 2002 Oldsmobile Aurora and 2001 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.
Lower the rear door window.
Remove rear door outer belt sealing strip from the rear door pinch weld flange, by gently pulling up, being careful not to distort the strip.
Fig 1: Removing Rear Door Outer Belt Sealing Strip