I've already had one headlight replaced due to this fault, and now it's happened to the other one.
I've tried putting dessicant behind the headlight - in the area exposed when the rear cover is unclipped, but to no avail. The headlight stays cloudy, the dessicant stays dry.
Surely the unit can't be so well sealed that the dessicant can't "see" the moisture?
Where does the moisture get in anyway?
-- Per ardua ad nauseam
Obviously I don't know about the C3 but my XM had the glass held onto the reflector by a series of clips. Between the reflector and the glass was a rubber seal. It could be that this seal is damaged. It might be worth running a bead of silicone around the joint. I should imagine that the bulb pretty much fills the hole in the back of the reflctor which is why your dessicant isn't working. I'd take the bulb out and blow a hairdrier into the hole for a few minutes to dry out the light. Replace the bulb then try sealant.
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