I normally use 3M adhesive remover, or PrepSol.
(both are great wax and grease removers also)
Recently I had removed some old door edge guards from an original paint truck.
It appeared that the door edge guards were installed with a very hard adhesive,... almost like contact cement.
No chemical worked on it.
Then I purchased a 3M eraser wheel that is used with a standard drill.
It worked great.
They are kinda pricey,... but it saved my original paint!
Check them out here:
http://solutions.3m.com/wps/portal/3...beSQSFJR0R56gl