Missing orange cover on marker light; Water leakage concerns

Most of these running lights are extremely cheap made in China fixtures. You might get lucky and find a replacement lens or just buy a new fixture and use the lens on the older unit if it fits.

Personally I would just replace the whole fixture. Yours seems to have a tungsten bulb that will eventually need to be replaced. The newer ones are LED and should last indefinitely. You can buy a replacement for roughly $3-7. And yes be sure to seal with new unit and do not rely on the rubber gasket.