I think you will find it not to work so hot, being a medium dry solven based acrylic enamel reducer. MM is a synthetic enamel, much more like, in fact probably is alkyd resin enamel. These used the equivelent of Dupont 3812 reducer but both hardware store lacquer thinner and mineral spirits thins MM enamels fine (great flow out with the LT). Conduct a test but I don't recall from my 1/1 days acrylic enamel reducer working properly in synthetic enamels. Just my take.
Many thanks, kinda what I suspected. How do you think it might perform with Testors lacquer dull and gloss coats?