C63 - privacy glass problem

[IainF]

Two or three weeks ago I parked the car overnight under a pine tree at a hotel. Next morning there were a few droplets of pine resin on the bodywork and on the tailgate window. They wouldn't come off with normal washing, so after I got home I got a cloth, dipped it in the petrol can, and dissolved them that way. No problems with the bodywork, but where I rubbed the cloth on the tailgate glass it seems to have lifted a bit of the tint, leaving a polarising effect below. I have tried washing this area, but it hasn't really helped. I suspect the tint must be applied to the external surface of the glass, and that I have dissolved some of it along with the resin. Anyone else made the same mistake, and do you know if it can be fixed?