Have you ever seen a sealed beam which allowed water to leak into it? Last week,(on my 1991 Grand Marquis) one of my headlights looked foggy, and when I tried to wipe it off, I discovered the water vapor was on the inside. I have never seen this happen before.
I replaced the bulb as I was afraid the water vapor might affect the quality of the light output or could cause the light to burn itself out since it was no longer sealed. The unit was a Philips Halogen H4656.
George