I went on a hunt through various craft stores on 82nd looking for a black Testers paint pen to touch up all the nicks and scapes on my cabinet decals. After a 3 hour adventure, I ended up only being able to special order it from "The Hobby Smith" on 33rd and sandy for $4. As most pins seem to have glossy black decals on the sides and front, this pen matches that finish/color pretty well. It also works great for the corners of the cabinet and where the legs attach as those are the most common spots for decals to peel and bare wood to show through. Testers is the one you want and you can only order it there, unless you wanna pay $10 for shipping online.
Elmers makes a black paint pen that seems to be available at any craft store that has a "flat" finish, so it looks funky if you use it on the decals. However, it works GREAT on coin doors. I know it may seem a little extreme to be touching up a coin door, but hey . . . you put in 15 minutes with that pen and the thing looks close to brand new.
If you're thinking about selling a game (or just want it to look purdy in your room), this costs next to nothing and adds a lot of value in the overall appearance.