My son has a 09 Audi A4 Black. He parks under trees all the time and I think he has sap stains all over the car. It looks like hard water spots all over the car. We washed it real good, the spot are there. I busted out the polisher and with a medium pad using Maguire's Ultimate Compound did nothing! The spots, stains are there. What can I do to remove these spots?