Testors used to make their own thinner. If its still available, have you tried that? I find using keeping brands together seems to work best. If its still made then try your local hobby store if you don't see it at one of the box stores.
The rack Didn't have the Testors thinner. I'm going tomorrow to a Hobby Shop near by (I'll call ahead to see if they have it). I Read about Mineral Spirits and Lacquer Thinner, also. I'm going to go straight Testors Thinning Solution. Who'd of thought mixing this stuff would be so touchy...
Its not working because turpenoid and winsor and newton thinners are made for oil based artist paints, like to do paintings, not enamel.
Like what was previously mentioned, you need to use mineral spirits if you dont use the testors thinner. You can also use the floquil or Humbrol thinners.