Each model of portlight seems to require a different thickness gasket, so I'd check in with Bomar if you have their portlights. The original gasket on mine was the kind with the flap that fit in between the lens and the frame. The replacement I got just sticks on the aluminum. So I trimmed back the old gasket just flush with edge of the aluminum as I didn't want to create an extra gap between the lens and its frame. Bomar sends good instructions with the gasket material.

I discovered that the socket screws for the handles were really too short for the thicker gasket material so I replaced the 1" screws with 1 1/4" screws. Those work well.

Unfortunately, the portlights still leaked, but not around the gasket. The water was going inside the lens frame. Bah. So I went down with my trusty bottle of "Captain Tolley's Creeping Crack Cure" and at 1/2 hr intervals squirted some on the exterior lip of the frame of the lens. Did that 3 times. It rained hard yesterday and I haven't been down to check yet. Not sure what my next step will be if it still leaks. Maybe a little bead of butyl tape ...