the sewing oil (or mineral oil) brisk rubbing and a soft rag, eventually softens up and sort of re hydrates the yellowed shellac. If you add a teeny spot of alcohol, it will melt the shellac quicker. That's what shellac thinner is, alcohol. The thing is, you can damage some decals so easily. I haven't tried Bug and Tar remover, yet. What does it smell like? Kerosene?