Help, have already tried an elbow grease spray and have taken off some of paint work through over rubbing.
I always used vegetable oil or some other cooking oil to loosen and remove adhesive. Put it on the spot where the tape is, and let it rest for a while. If it is normal masking tape, that is, made of paper, the oil should pass through it to the adhesive. Once it encounters the adhesive, which is oil based it will dissolve it.
After waiting, rub it with your finger (no scratching!). The tape and adhesive should ball up and fall off.
I had really good success with WD-40 to remove old hardened gunk from duct tape (used to prevent a broken power window from sliding down). It worked great for removing the residue from the glass and car body.
Diethyl Ether is an excellent solvent for many contact adhesives, and does not attack most original auto paints (though it might remove touch-up paint or lacquer). However, it is extremely flammable, easily ignited by just the heat from the engine or muffler even after the car has been shut for a while.
If you do want to try it, most pressurized engine starter sprays contain a high proportion of ether, and there is no danger of flashback (flame going back into the container).
Work outdoors, away from anything flammable such as a house or dried grass. Do not wear clothing that might easily catch fire.
Make sure the car engine is cool and avoid turning on or off electrical devices (e.g. opening a car door, which turns on dome light).
Test the ether spray on an inconspicuous spot to see if it attacks paint. Use only a brief spray.
Spray directly on the masking tape and peel before it dries, in just a few seconds. Again, work on only a small area at a time that can be treated with a brief spray.
Spray ether on the "stickum" left on the finish after removing the tape and wipe the finish immediately with fresh cloth or paper towels; repeat as needed.
N.B. This is potentially dangerous. Though I've safely used ether to remove tape residue, your safety cannot be guaranteed.
Try something like the Spot-X No Scratch Pad with a liberal amount of alcohol. If alcohol doesn't cut it, try acetone (commonly sold as nail polish remover, be sure and get the clear variety) instead. Do it in the shade / indoors, allow the liquid to penetrate fully ...
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