Bought a 2009 SLK 300 three months ago. So far we are loving it. Was washing it this morning and discovered that I need front mud flaps. I will check with local dealer to see what they have. Meantime I am trying to remove the gunk (tire bits or road tar or whatever it is) and the only thing that seems to work is scraping with my fingernail. Any ideas on shortcut that will actually remove this stuff without ruining the paint?