Ten plus years back our middle son had an used  Ford Escort  at
college.  It had the same problem with one of the headlights.  The fix
was simple as it turned out.  During spring brake I faced the front of
the car into the sun, did not think of the hair dryer, until all of
the water evaporated.  I removed the grill  from around the
light/reflector/lens and put a thin layer of clear silicone calk
where the lens and reflector met. This from a small hand squeeze tube
not from a caulking gun.  I also put some on my finger and ran it
around the whole where the bulb went in.  I let it dry before I put
the bulb back in.  Never had the problem again.  His college BTW was
in the mountains of Virginia so it got a fair amount of snow, rain,
and dampness.