pdp76

I've been trying to remove some paint off a model car with "Purple Power" as many people have suggested in this thread. After soaking for many hours (sometimes up to 72 hours at a time) repeatedly over the past 2 weeks, most of the paint came off with some scrubbing using a scouring pad after the soak. However, there is still a thin layer of the paint, it almost looks like a stain, which doesn't seem to want to come off with gentle scrubbing of the scouring pad. I have to use my fingernail and dig into it a bit before this thin layer comes off. The plastic thank goodness isn't damaged, but I'd hate to have to use my fingernail, or something similar, to remove this final thin layer of paint. From what I understand, after soaking in Purple Power, the paint should come off very easily... and it did for the most part except for the last thin layer. So I'm wondering why I'm having such a hard time? It is the type of paint that was used? http://www.testors.com/category/136961/ I'm not sure what kind of plastic it is, but the model was made in 1990, but perhaps the type of plastic might make a difference? Another thought I had was that the Purple Power I used has lost its potency over the 2 weeks, but from what I understand, that stuff doesn't lose potency very easily. Any ideas to help me completely strip the paint of the model would be appreciated!