Re-flashing a damaged vent has several problems. First, its not going to last, the squirrels will chew it off again. Even if a screen is put on its no gurantee they wont gnaw the base of the vent, then you have a serious leak. Second, the roofer may discover that your roof decking is rotted and will want to replace it. So a 50-100 dollar per vent repair just went to a few hundred per vent. Lastly, the shingles have to be pulled up when re-flashing, and often they simply never look the same.
So instead of re-flashing, just slide on a Critter Quitter. The vent is protected, the leak is stopped by our patent pending design, and there is no need to pull shingles or expose decking. Plus its a lot less expensive and looks better.