I bought a truck that had belonged to a business and they had applied stick on lettering, individual letters, on both doors, the fenders and the front bumper. Some of the lettering has been peeled off for quite some time but the glue was not cleaned off and over time has collected dirt and grime. How do I get rid of the glue residue? I have tried WD 40, a sharp razor, and mineral spirits. After much scrubbing, cussing, and scraping, and some paint gouging, I got most of it off of one door, but you can still see the "ghost" of the letters, any suggestions? I do plan on giving it a sanding, priming and a poor boy paint job. Thanks for any suggestions.