I had this problem after replacing the side light bulb which is part of the integral lamp unit. The headlamp unit is supposed to be airtight so as to prevent condensation on the inside caused by cold damp air on the outside reacting with the heat inside the lamp when headlights are on. The fault can also be caused by a crack in the glass unit itself. To dry out the unit first make sure the bulbs are a tight fit and that the round plastic cover that encloses the the rear of the lamp unit is seated correctly. Cover the headlamp with a large sheet of white card or towel etc. Then switch the headlights on full beam so the light/heat from the lamps is reflected back and not allowed to show as normal. This concentration of heat may dissipate the moisture inside the lamp unit, especially if done on a hot, sunny day. Do not overdo this heating up as the unit can get very hot when the light/heat is reflected back in this way. Mine took a couple of attempts to get right but seems fine now.
alan, April 2012
