You can also try laquer thinner sold at many auto parts stores available in quart and gallon size. A quart should be enough and usually works real well removing spray can paint, wipe or brush on just like cleaning greasy parts, wipe excess, the stuff dries almost instantly, you may have to do this 2-3 times and your ready to paint with a nice clean surface. Laquer thinner is very flammable, use rubber gloves if you can and use in ventilated area. Note, it usually does not remove any factory paint, the Buick intakes have some kind of whitish epoxy coating from the factory and is very durable and makes a good base to paint over, after wiping intake down with laquer thinner you will have this white coating still there, paint over it and you should be set, good luck!