If I may: Very good touch up is one of the most difficult things to accomplish, IMO. Paint applied with a small brush is usually lumpy compared with the sprayed finish next to it. The only way to avoid this is to lay on light layers of paint, very thin, and lightly sand with tiny strips of 600 to 1500 paper after the coats are dry. Good and dry, which takes as long as 3 weeks sometimes but you can usually lightly sand after a couple of days. Build up the spots so they're just proud of the sprayed surface then smooth it down to meet the level surface and blend it in. Then, to bring the shine up hit it with rubbing and then polishing compound. It's a LOT of work to do it right. An airbrush and masks help, but it's still a lot of work.