You may not think a vent could leak that much if the flashing has been chewed off. But its really a significant leak. A flashing is about an inch wider than the internal diameter of the vent. So a 1 1/2 inch vent has a 2 1/2 inch flashing that means that the gap between the outside of the vent pipe and the flashing is about 3/4 of an inch. If you measure that out, the area open to leaking is about the same as the vent pipe itself. Its a little less for the larger 2 and 3 inch vents, but its a heck of a lot of water getting into your decking and attic. Critter Quitters will stop this for a very affordable price.