The headlight is working again.
After taking off the front bumper and removing the driver's side headlight, I had to completely disassemble the headlight itself to change out the ballast. The ballast itself was accessible via a panel on the bottom of the headlight, but the part which plugged in to the bulb wouldn't fit between the reflector and the body of the headlight.
I needed to remove the lens off the front, which was mainly secured by silicone sealant. to loosen the sealant, I baked the headlight in the oven at 220 degrees for 8 minutes. I could start to get it loose at that point, but it required two more sessions in the oven, 2 minutes each, before I got it off fully.
[caption id="attachment_19294” align="alignnone” width="300” caption="Completely disassembled headlight”][/caption]
The reflector was held on by the adjustment screws which are used to align the headlight. I recorded the position of the bottom screw, but by the time I realized what they were for, I had already moved the top screw. I think I've gotten them back to close to the original position, but eventually I want to perform the full calibration procedure from the service manual.
[caption id="attachment_19308” align="alignnone” width="300” caption="The worn-out ballast."][/caption]
[caption id="attachment_19295” align="alignnone” width="300” caption="test, just before reassembling”][/caption]