Cleaning Experiment - Dried on Adhesive Goo

Sticky residue is a pain to remove on a good day. Forget it when you try to get it off after it's been dried on for months or even years! Sandpaper would do the trick but it's not always, or almost never, the answer because of the damage it does to surfaces.

Here's my window under my AC unit. That black stuff is adhesive left behind from plastic coverings from several winters of two sided tape that held it on the frame.