Touching up paint job

That's the good stuff, about the best there is IMO.

Before masking a surface, make sure it's clean and free from oil from handling. I like to clean parts with alcohol before painting or masking but DO NOT get alky on acrylic paint as it can dissolve it.

Also be sure to make sure the edges are well and truly stuck to the plastic before painting. You can get a burnishing tool from an art or craft supply store, but a thumbnail, toothpick, piece of sprue with the end round off, anything like that will work just as well. Just rub over the edges of the tape real well to make sure they are stuck.

If you lay your tape on the bench, the edges can pick up sanding dust, lint, etc. from the table. Put a strip on a hard surface, like a piece of glass, and use a straight edge and X-Acto knife to trim the edge off. That will insure that the edge you are sticking down doesn't have dust on it that will let it lift from the plastic.

Tamiya tape will stick very well, but you have to give it some help or it can leak.

Thanks guys. I'm using Tamiya tape, is there a better tape that will stick to the model a little better.

If the area is very small or in an area that is not very noticeable I might try hand brushing, but otherwise I'd probably airbrush it just to keep it from looking different.

Later ... Rick posted his response while I was writing mine. He has a very good point regarding the buildup.

Brushing will very likely mess up the paint job if it's an airbrushed finish. Don't know how severe your seepage problem is but if there isn't much paint build up you could try reverse masking and respraying the originally masked area to cover the seepage. If you have enough paint build up that it would be visible, best bet is to lightly sand it smooth, respray the original color, remask and respray the second color. Problem is easier to fix with flat paints than with gloss.