I used some partial clear touch ups with some acrylic clear and it held up just ok. Painting it on by hand would be difficult. Airbrushing is the way to go but I understand it can be challenging for some. Have you thought of a playfield protector? The new types are very good and have a nice shine to them. It would also protect the touched up paint and make the playfield look like it was clear coated. I recently played a friends pin that had a protector and it looked like a new Playfield.