UPDATE: We've had very little rain in SoCal since the Christmas night downpour although the overnight low temp usually drops below the dew point, and since I sponged out the water at the bottom of the housing and used a hair dryer to thoroughly dry them out via the rear access panel, there has been no more water intrusion.

I even used a spray bottle and thoroughly doused them around the periphery of the lens, but the interiors stayed dry.

So the point of water intrusion remains a mystery, but I will continue to monitor.

In the process one of the H4 bulb low beam filaments broke. I bought two Hella H4 bulbs on Amazon, $3.25 each and replaced both keeping the serviceable one as a spare. These Euro headlights are actually over 35 years old since I first installed them on my '84 190E 2.3, and then transferred them to the '88 2.6, so the bulbs had good longevity. I don't do much night driving nowadays.

Duke