Mth engine paint

You might want to describe what color you are interested in.

Might try Scalecoat Loco black was not too glossy and not too flat.

I have always used Scalecoat Loco Black, especially on all the drivers and running gear components on steam locomotive models.

Touch-Up as in minor scratches, etc. or repainting it?

For small blems I use a Sharpie black marker......works for me!!

Me too, hence the question. 

I actually have a set of different colored markers.  Sometimes they match really well, other times not so good.  However, it's easy to try it and see if I can fix it simply.

Scalecoat makes a black touchup marker. I ran across mine yesterday while looking for something else. I'd forgotten I had it. Most any flat or satin black paint will do for a near-invisible touchup on a steam locomotive.