Originally Posted By: The Critic
Strong degreaser + brush, or lacquer thinner. Lacquer thinner works best though.
Don't use lacquer thinner, it may be incompatible with certain plastics and it can turn black vinyl trim gummy in fact you might end up with little fibers from your cloth bonding to the gummed up trim, it'll ruin the plastic tailights, necessitating compounding or if left to soak wetsanding.
I think you may be thinking paint thinner, aka mineral spirits. That is safe, and also evaporates much slower. A toothbrush and mineral spirits will work at removing the white staining. In my experience it is the best way, better than degreasers even.