If you have a vent leak, its probably not going to show up in your ceiling unless its really bad. It will slowly soak your decking down and over the life of the roof rot it significantly. Sometimes they actually cave in, but usually you just get a knock on your door when you reroof and a big bill for new decking. Critter Quitters cant repair damaged decking, but they will stop further damage. So why take a chance, order some from Homedepot.com, Amazon, or have any of our installers put them on if you are in their service areas.