The tape is a rubberized product. It should be a tight fit. You use oil during (to ease) installation so that the tape swells (due to the oil) and locks the glass in place. Then, if the glass is broken in the future, gasoline or similar solvent will attack the rubber tape and cause it to let go of its hold. If you use glue/sealant, clean-up to replace the glass will be difficult and time consuming.
