Posey looks lovely with her new hair
![Smile :)](https://mlparena.com/Smileys/default/smile_001.gif)
Unfortunately I would say at this point that you are right and the stain is going no where. As long as a stain is on the surface of the plastic then it will be removable - however sometimes stains literally recolour the plastic and get into the plastic pores, when that happens there is no moving it.
As for Gusty have you tried setting her hair with boiling water, wrap a stocking over it to hold it in place, put her in a zip lock and then pop her in the freezer for a couple of weeks?