That is one way, or you can simply use a hair dryer on the vent and see if it will help loosen, by melting, the area. You may also use a household remedy I suggest all the time, on just about everything, baking soda and lime juice. It will bubble and help eat through grease and grime. See if that helps you and let me know the outcome. Also too, with dryers reaching up to 150ºF it can burn the coating on the vent and cause discoloration too. You may find out that it is burnt coating and not any residue so to speak. Let me know!