I don't know if you can get it in the US but Eucalyptus oil is magic on sticky stuff. I use it whenever I get glue on my skin. It even says on the bottle it can be used to remove tar. You will smell like a Koala for hours
A previous owner "patched" a large hole in the roof of my standy with roofing tar. I finally got it off with a propane torch (Bernzomatic) with a flame spreader, and a metal bladed paint scraper. I finished with some mineral spirits (paint thinner) and the result was smooth enough for me to install a proper patch bedded in butyl tape.