This is what a lead flashing that is damaged looks like close up. As you can see, the lead has been chewed off the top and the area between the pipe and the lead is now open to rain. This will soak the decking under the shingles and rot it over time. In worst cases it spots the ceiling. Critter Quitters drop the rain down the center of the vent keeping the damaged portion dry, thus repairing the leak. Why pull shingles and put a new flashing on when Critter Quitters will fix it for half the price.