Open the hood and on the side facing the engine you'll see the gray oval tube that is the vent. It is not a sealed system. The clear lens is pretty well glued to the black plastic and unless the bulb has been replaced, the back of the housing (that is supposed to be removeable) is stuck hard onto the rear of the housing. Perhaps the vent tube has been knocked off/out or the rear seal is allowing water in?
Well, even if the rear seal wasn't sealing, it should let the condensation out - the fact the condensation is staying there might imply it is actually sealed - i.e., the vent is blocked. I've had the backs off of my headlight housings on both Vipers many times (putting HID's in, aiming them a couple of times) - the first time you remove the back it is usually stuck on because they use a soft/tacky sealant, and it returns to that stuck-on state after being on for a while. But, that is more of a dust prevention than anything else.
So, remove the back of the one with the condensation - its fairly trivial to do once you remove the six plastic wing nuts holding the wheel well hatch in place, then the three metal wing nuts on the back, and loosen one (or is it two?) captive thinner wingnuts on the back - pry it off from the sticky seal, and take a hair dryer to it.
