Ah my friend, I had the EXACT same problem just a short while ago, except my headlight would go down, but not up.
The forums didn't provide much help <img src="http://www.zilvia.net/f/iB_html/non-cgi/emoticons/mad.gif" border="0" valign="absmiddle" alt=':angry:'> so I had to set upon the task myself.
After about 4 hours of troubleshooting I figured out and fixed the problem.
First off, it's an electrical problem, not mechanical, so you can put away the liquid wrench. Secondly, this is only my solution pertaining to my problem, your electrical bug may be located elsewhere.
For me, the problem was found after I pried open the wire connector (follow the electrical wire coming from the motor until you find a connector). When I opened it I eventually found out that among all the pins, two of them carry 12 volts. One to give power to open the headlight, and one to give power to close it. Soon after I realized that, I saw that the pin, which provides 12 volts to open the light, was corroded and had fallen off, thus not giving the motor power. So, all I needed to do was pull it out from the connector, strip it, get another wire as an extension, and solder the connection back up.
After that, I pushed the button, and bingo! Both came up and both came down.