BMW 2000 323i, automatic transmission(steptronic).
Every once in a while, my headlights
work properly, but usually my driver-side xenon headlight(low-beam) is out, (high-beam halogens still working fine) and am forced to take my shop truck out into the night.
Have checked the xenon bulbs, and replaced both the ignitor and ballast, and the problem persists. The bulb and ignitor contact points are pristine.
In most recent events, after it not having worked continuously for about 6 months, I tried swapping over the xenon bulb from my passenger side just to troubleshoot, and it did
not work, so I swapped it back to the passenger side. Later that evening, I went back to troubleshoot some more, and the xenon low-beam
worked with the bulb that has been in there for the passed 6 months! As I drove into town, it went out again

What's the deal here? Wiring issue? And where? Do I need to get an entire new headlamp assembly or is this possible wiring business something a mechanic can do?
Thanks!