I just picked up a cheap G1 toy and plan to redo all the stickers but want to check the best way to remove the old ones without doing too much damage?
I would say get yourself a soft sponge, and some luke warm water, and just gently rub on them until they go away. It would take a lot of patience because you'd have to keep gently rubbing and it would probably take awhile, maybe even a couple days. Make sure to dry all the water off between sessions.
Okay, on PM Prime, those stickers are actually paper with foil printed on them. This was the point that they were really getting away from the more expensive mylar stickers. You can try "goo gone", which should get them off fairly clean. Then soap and water to rinse the areas off.