The repair can be done; I just did two. It is easy once you know how, and requires special tools:
1) Pop the head off the fixture with a flat screwdriver.
2) Open the head, remove the bulb, the counterweight, and the wire.
3) Next to the outside nut (on the shaft), jam a small screwdriver to create friction.
4) Use a small wrench (5mm) to loosen the inside nut.
5) Remove shaft from head.
6) Using wire brush on rotary tool, restore shaft to shiny metal.
7) Using rotary tool, remove oxidation and carbon inside sheet metal conducting surface.
8) Reassemble.
Total time: 10 minutes (once you know how).
Onerous Ethic, January 2010