That depends entirely on what plastic it is. Most air-brush parts that are plastic are one of the essentially inert plastics (like Delrin™) and impervious to the solvents commonly found in lacquer thinners. It also depends to a lesser extent on the solvent blend in the lacquer thinner. Some are more aggressive than others.
The term "plastic" covers a host of synthetics that numbers in the thousands, and keeps growing.