Xylene works pretty good for that God awful white plastic. Soak a rag with it and let the rag sit on the plastic for a few minutes. Then use a heat gun and a razor blade for the stubborn parts. My parts sat for 10 years before I bought the kit, so I know what you're dealing with.
Step 1. Start with the gentlest approach -- warm water and a damp cloth. Wet the cloth and rub it over the dried-out tape. Allow the water to soak in for a few minutes, then carefully peel back the tape. Re-moisturizing the surface should help soften the glue and loosen the paper tape. You may need to use a razor blade to remove any sticky residue. I really hate seeing aluminum pieces lose its coating. And if you tried to remove it, without scratching it, you know it's a very long process. This video 5. Give mayonnaise a try to soften and remove the adhesive. Carefully apply a very thin layer of mayo over the leftover glue on your screen. You can do this with your finger, or put the mayo on a clean lint-free cloth and wipe it onto the screen. Leave it alone for about 20 minutes, and then gently rub away the glue. gojAxO.