I believe the problem is metal fatigue or corrosion on the fixture contacts where the bulb rests. I have twice already cleaned and reset the bottom metal leaf contacts and wire loops on the side. Each time I get a few thousand miles before it begins to fail again, usually when it rains although there is no visible sign of moisture entering the socket.
Can anybody tell me the part number and best place to purchase? It is one minute planned labor which is always better than an unplanned failure.