Is it possible, even likely, that someone who cleaned, lubricated, and reassembled the motor back in 1995 (and even stuck their own sticker on the refurbished motor case) inadvertently left out the c-clip?
In this scenario, the headlamp / motor system worked fine for about 2-3 months, and then the road vibration moved the pinion gear out of alignment?
But that was never noticed, because the car was only driven in the daytime.
Then one night, the owner wanted to drive home from the bar, and his lights wouldn't come up.
So eventually, these things (and other, more serious issues) led to the car being parked, and neglected, until the new owner snapped up the car for a song.
Now, the new owner is contentiously fixing the problems not fixed by the PO, and finds this unusual situation?