There must be some solvent you can use. Paint thinner or acetone might work, my friend got paint thinner to eat through the glass adhesive that held the halfs together of a sealed beam halogen light. also maybe an automotive degreaser. I've gotten alot of stuff loose that I never thought would come off that way, although it's hard to find a good degreaser. Some of them do little more than soap, but some will burn your hands if you dont wear gloves. one that i know is really strong is "purple power". it sounds fruity, yeah, but it will eat through just about anything other than the metal itself. You should be able to find it in an Advance Auto Parts or something like that.