I thought I would just throw this out there, for those of you who don't subscribe to any online auto forums, or have the information at hand.
When you purchase aftermarket lighting, unless it is absolutely 100% Origional Equipment, don't expect it to be perfect. Most headlights, especially the cheaper plastic housing and plastic lense models like the "Halo" or "Projector" lenses for older and newer automobiles, will often leak or fog.
Because these items are subjected to high heat and weather of all sorts, there's no guarentee that your set won't experience some fogging, or even gather water over time. The absolute best way to make sure you cut down, or sometimes totaly eliminate leakage is to reseal the housings yourself.
Common sense will lead you in the right direction, just inspect your new lighting devices, and see where the factory placed it's sealant. If a section looks leaky, or not as tight as you would like it to be, use some clear or black silicone, available at nearly any autopart store, to strengthen the seal.
Sellers of these items can't really prevent this from happening since these parts are being shipped straight from the factory in many cases, but you can prevent it by taking the extra step yourself.
So, unless the vendor says clearly in their auction "will not leak", or "leak proof", etc.. assume your set will probably not be 100% leakproof.