I would be willing to bet pink is from wet insulation. Just been through a couple leak problems-first in ten years, and when the insulation gets wet that seems to be one aspect of problem. As you are about to learn, it can be a real nightmare finding where the leak is. If you think it is the vent and recaulk that area and solve your problem count your blessings!! Trust me, it won't be that simple next time. Ha!!