If it's condensation, try removing the bulbs, and as I did, use the blower function of a workshop vaccum cleaner to blow through one of the orifices. ( Presuming you can blow clean air!) The air from the blower is usually warmer, so it'll clear the moisture after a while.
I'm not 100% convinced it is condensation. It's not like fine water bubbles it's milky grey mainly at the top edge. I have power next to where it is parked so I will try a hairdryer on it tomorrow and see how I get on.
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