I ran into this with my Dynamo cab. When I got it, the CP was covered with vinyl that was printed to resemble astroturf. The vinyl peeled off fairly easily, but the adhesive residue it left behind was a ---smurfette--- to clean off. I ended up using xylene and razor blades to clean it. I'd soften the stuff by wiping it with a xylene soaked rag, then scrape the residue off before the solvent evaporated and it became sticky again.
Once all that was gone, I bead blasted the CP to remove all the rust, filled a button hole I didn't want, primed it and did a little body work on it. I'm currently in the process of painting it, haven't decided on whether I'll do artwork or just cover it in textured vinyl.