Touching up using aerosols is an art, particularly if it's metallic. It takes a great deal of patience, time and practice. Try on some pieces of scrap metal or similar until you have the knack. If we don't try, we'll never learn but you don't want to ruin your pride and joy. You could always get a quote from a professional if your motor is half decent. If it's just a runabout it may be worth a go. If you do have a go, apply in thin coats, leave it a good time between coats or you will get runs (in the paint, not to the toilet), and read the safety instructions as most paints are veeerrry toxic! Don't forget to use T-cut or similar to remove the roughness and overspray.Enjoy.