Wow, you actually found a THP car on a lot?! It was probably a customer order gone wrong and they got stuck with it. Very hard to find THP as a dealer order. Anyway, given how long it has been sitting, 10% is a good starting point. They will probably counter at 5%, meet in the middle at 8%. *shrug*
If it has EXACTLY what you want, be prepared to be less stingy though. As I said, THP is really hard to find.
I had found "the one" I wanted and spent a few days waiting for crappy sales manager to get back to me (they had to get it from another dealer). By the time he did, it was gone.
lesson learned. This late in the year, be aggressive.
Bozman