If you have very small places that you need to touch up, go to your local auto parts store and try to find a color that is close. You have to use the brush that is usually supplied with the paint. You can't spray it.
Usually only the engine cases can be repainted in black with high-temp paint sold at auto parts or even barbecue paint. Either you remove all the black with paint remover, or you use a degreaser and feather edge (sand) the spots, scuff the whole cover and respray.
If you don't understand any on the terms or what I am talking about, research the net. It's all there