I have made a set of gaskets out of light gray RTV Silicone rubber (elastomer). Both the aluminum housing and the plastic lens need to be very clean. Apply a generous amount of the RTV to the bottom surface of the housing (be sure to apply around the two screw holes too) and place the lens in place. Hold the lens in place with the two screws with only a very small amount of pressure. Let cure for a day or so. When cured, the lens can be pulled out and the newly formed gasket can be gently removed from the aluminum housing. This process took me a couple of attempts to get good sealing gaskets but I worked for me. I used a old lens to make the gasket so I would not harm a good lens in the process.