This is what I use to remover sap, tar, leftover glue and wax before I wax my car. Safe on plastics and mostly all paints. You can buy the Nason Silicone and Wax remover at many auto parts store. Norton also carries similar products and the high end RM line was discontinued because of the high volatility/toxicity and the new laws/reform with water based paints. I bought mine at UAP NAPA in Canada.
Best stuff for the job, don't forget to wax again since it removes wax.
edit: a gallon runs around 23 to 30$ CAD, good for a VERY long time.