I am (slowly) working on converting a Porsche 917 without the little fins in the back to one with them. I purchased the Fly 917 kit (Buenos Aires) and had to strip the decals/tampo off to get a clean white body. However, soaking in Simple Green for over a week didn't remove a thing. Rubbing alcohol worked with equally bad results. What did the trick for me was rubbing the tampo print with a cotton tip soaked in brake fluid. Make sure you wear gloves as brake fluid sucks the moisture right out of your skin. The body paint is still spotless but the tampo print is gone.
I found this method googling for "stripping model kits" and this was one of the methods. There are videos available showing the process. Supposedly soaking them in lye works great too, but finding lye based cleaners at the (ACE) hardware store was a little challenging. Oven cleaners are usually lye based but I wasn't too sure about the other compounds in it, even though people on the web recommended it for stripping model kits. Using the brake fluid soaked cotton tip I had a little more control over the amount I applied. I left a couple of tampo prints I liked on.
After the brake fluid treatment wash the body in mild soapy water and rinse thoroughly.
I did have another body that had water slide decals on and they came off like a charm using Simple Green.
George
--
"Get the shotgun, Martha. The herd needs a thinnin'." - Bucky Katt