2002 Jetta Headlamp Bulb Dimming Mysteriously

Problem: I realized my right headlamp bulb, although not completely out, was substantially dimmer than it should be. I replaced the bulb and it was fine the first time I turned the lights on to check after replacement. I noticed the very next day that the new one was dim. I replaced it again after talking to the auto parts guy who said to be careful not to touch the glass on the bulb (something with finger oils). I wore rubber gloves and replaced the bulb. Same scenario - worked fine at first then turned dim again. This is true whether it's just the daytime running lights or with the headlight switch turned on.

Causes:
1. Cheap aftermarket bulbs? Maybe, but two in a row is more than coincidence usually.
2. Poor installation? Maybe I am doing something wrong, but I was exremely careful the second time around and did not touch the glass the second time. Also, the bulb was the correct brightness immediately after install.
3. Electrical Problem? I hope not as electrical problems on a 5 y/o car would suck immensely.
4. Demon Possession? I'll burn incense and candles tonight.
5. Could a cracked light cover be a problem? Do these bulbs require an airtight environment?

If anyone has any ideas or experience with this, PLEASE share them with me.

Thanks,
Mark

I don't know if you have resolved this issue but here are a few ideas. Try the new bulb in the left side. If it works fine its not the bulb. My guess is the bulb is fine and wiring is the problem. With a Digital Multi Meter check the voltage at the bulb socket. My guess is it will read < 12 volts. then start tracing the wire for a break.