For years I have used this stuff on vehicles, since the early 90's. It's tough to find, the first place I saw it was this Mustang site. Last time I needed it I bought 8 jars and am still working through that supply.
http://www.mustangsplus.com/xcart/No...er-Powder.html" rel="nofollow" target="_blank">http://<a href="http://www.mustangsp...owder.html</a>
It pretty much takes the surface back down to glass and removed all residue. If you were nearby if give ya some to try.
If you have after market tinting test it on a small area first, it might tear the film up. Raw glass this stuff does wonders, also good on glass shower doors and gunked up fixtures (used it when we bought a new house). Shines everything up to look like new.
It takes some elbow grease, so don't expect it to take just a couple of minutes. I probably spent 30 minutes on a windshield with minor build-up, but it looked great when I was done.
-Chad