So the fogging is part of the design in an intricate, over-complicated German-engineered headlight module ventilation system.
In the Odyssey, I had a tailight filling up with water. I removed it from the van, drained the water out, left it overnight on a floor vent to dry, sealed it with clear silicone the day after and reinstalled, along the joint between the clear plastic and grey backing. No more water.
Never had fog in the Golf's headlights.