I would look at the grounding wires for the headlamps - usually one for each side.
The connections can be corroded, loose or even the wires broken given the age.
Based on some of the issues you mention then that is a possible cause that I have seen before.
Using a Phillips head screwdriver, loosen the screw holding the wire clip. Pivot the wire clip upwards. If the clip won't pivot up, remove the screw; then pivot or remove the clip. When the clip is out of the way, the bulb can be removed.