If Novus #3 won't remove it, I would imagine options are to live with it, replace it, or wetsand / rubbing compound and move your way down the abrasives ladder to less and less abrasive until its perfect.
Okay, addressing your concern, a rubbing compound seems more in line with what you need. Do you have Finesse-It II or
Meguiar's #2? Someone compare abrasiveness of Novus 3 (most abrasive) with one of these products? They work on plastic too.