And if the above suggestions don't work...
I've removed some pretty old highway-line paint using FK1119, with an extended dwell-time. Somebody like Ron Ketcham could probably offer caveats about letting that stuff dwell for too long, but it worked fine for me.
And they sell "highway paint remover" products (check TOL, I think they have one), but I've never tried them.
True Confessions time...I have some highway paint in the one wheelwell of my wife's A8 that I never did get off...doesn't bother her, so it doesn't bother me.