Remove the moldings surrounding the glass.
Have your assistant stand outside and support the glass.
Working from the inside truck, start at one upper corner and work the weatherstripping across the top of the glass, pulling the weatherstripping down and pushing outward on the glass until your assistant can grab the glass and lift it out.
Clean the weatherstripping, glass and glass opening with solvent to remove all old sealer.
Apply liquid butyl sealer, in the glass channel of the weatherstripping and install the weatherstripping on the glass.
Apply a bead of sealer to the opening flange and in the inner flange crevice of the weatherstripping lip.
Place a length of strong cord, such as butcher's twine, in the flange crevice of the weatherstripping. The cord should go all the way around the weatherstripping with the ends, about 18 in. (457mm) long each, hanging down together at the bottom center of the window.
Apply soapy water to the weatherstripping lip.
Have your assistant position the window assembly in the channel from the outside, applying firm inward pressure.
From inside, you guide the lip of the weatherstripping into place using the cord, working each end alternately, until the window is locked in place.
Remove the cord, clean the glass and weatherstripping of excess sealer and leak test the window.
Install the moldings.