[jmk]

If you can peel out the screen and gasket and remove the screen from the gasket without tearing up the gasket too much, you can just get some new screen and bed the new gasket and screen in place using marine silicone. I did all my port lights this way and they came out perfect. Below is the McMaster Carr order for the screen. It's important you get this type. It's non corrosive and matches the original perfectly.

1017A53 Fiberglass Insect Screening, Medium-gray, .011" Wire, 24" Width, 7' Length