@Sal V have you checked out the Krylon Gloss Navy that @Roy O had suggested? How does it match up with the existing color? Would you be satisfied with that color and the visibility of it when corrected? What does the nick look like? The question I would have to ask myself is, am I running this train, do my kids run my trains or is this a shelf queen? If I’m not happy with the Krylon match and still want to touch up the nick I would invest in a can of Henning’s Collector Colors. Check the match than make my decision to leave the character alone on the engine and just enjoy or attempt the touch up with a appropriate size brush.