Ford's factory assembly manuals and shop manuals indicate the proper way to install a windshield or backlite. You need to use a thin bead of butyl seal (nonhardened, gooey, petroleum-based caulk) in the inner and outer grooves of the gaskets. All window-trim clips should also receive a dose of this sealer, as shown in the illustration. This handles the foundation of your installation. Once the glass is installed and seated, pump as much sealer between the gasket and the body as you dare, then install the trim.