Sure, pop out the bulb (I suggest removing the bulb from the harness and putting it somewhere safe while working on the assembly), then use a clean cloth damp with 91% or better alcohol and a wood/plastic rod to wipe around inside the assembly. Try to just hit the lens with it and not the reflector on the backside. You can use a hairdryer on low to blow inside and evaporate anything the alcohol doesn't get, but it will probably leave minor water spots. Use some clear silicone or something to seal up where the water leaked in. Reinstall clear bulb, wait until the silicone dries to use the headlights, and you're done. You might want to seal up the other headlight in the same spot as well.