Dimming Right Headlight on '89 300E

i have a 1989 300e and i have been running 45/65 hyperwhites on them for about 3 months now...however, recently the left one jus dims to a weak yellowish-white color...i know the bulb is fine cuz i switched over the right bulb (which works fine in the right headlamp assembly) and the same dimming occurs...i am suspecting an electrical connection problem but have no idea how to approach solving it...any suggestions would be appreciated....oh, in the past when this happened i would just have to lightly tap the headlight lens and the bulb would return to its 45w brightness again...What kind of repair would be needed to fix the problem? Thanks