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One more thought to conect the dots from the OP. Since the problem area is close to the outside ("The area is near an opening in the exterior wall"), then this is another indicator that is a thermal issue and more insulation may help. if possible, put a rigid deflector to keep the outside air that is entering the attic for ventilation from passing over the problem area. the convection of that cold outside air can certainly lower the temp of the vapor barrier on the attic side (think of it as wind chill since you live in northern IL).