the TF headlight lenses are sealed to the back part with a bitumen type material. it is possible to take them apart by heating the whole headlight up in an oven at a lowish temp. It is then possible to remove the old seal material and apply new. I did this when I installed DRL's in my headlights. I bought new seal material from Fleabay. Not had any issues with condensation. interestingly, I don't think the headlights are a hermetically sealed as there arw two large access holes at the rear to enable bulbs to be changed, these holes are closed off with two large rubber stoppers, are your stoppers properly installed?