From the experimentation I've done with the MM Acryl paints, just trying to figure out how to airbrush them without constant clogging in a high-altitude/low humidity environment, they actually responded very well to being thinned with ammonia. So, my guess is that MM Acryl paints have an ammonia component to them which will remove just about every other paint if it goes on wet. Have you tried airbrushing it? Personally, I like to use the good old fashioned Testors, lacquer based, Dull Cote and Gloss Cote clear coats. A lot less hassle to airbrush, and not as damaging as ammonia. Still have to airbrush it though, or it will lift whatever paint is underneath it if it goes on wet (like from a brush).