Stick with enamel. Stay away from anything that is water soluble - it won't be as durable. Do a test in a small area that is not so visual. Depending on what you are covering I would suggest a matt/flat black Humbrol, available at better hobby shops. Also, if you can, I suggest using the same technique as automotive painters when doing a touch up - sanding to feather the existing paint down to the substrate, then mask and airbrush the paint onto the bare area, allowing the paint to dry between two or three coats. Clearcoating is optional based on overall finish.
Do not expect it to look like it just came out of the box, but like we used to say after painting our RC car bodies... "It's a 10!" meaning from 10 feet away going 10 miles an hour, it looks good.
Edited by Peter, 03 May 2017 - 07:45 PM.