Sorry, my last one was an 86 and it had the gasket. They make a tool for removing it, but to clean up the mess that you have now, use a heat gun to soften the old mastic and work it away with a plastic or nylon scraper. Clean up with solvent. Have one of those glass installers remove other window with their tool or find someone to borrow theirs; probably a body man. Get enough mastic from the glass company or go to Lowes and get a caulking tube of silicone to reinstall. You'll need to hold glass in place with some blocks or duct tape for a day or two till it sets up. A used sliding rear window would be a nice addition.