My 1991 740 wagon spends a lot of time parked beneath Chicago's elevated train tracks. Wax doesn't keep the tiny flecks of _________ from sticking all over the roof & hood, though it helps. The offending substance is not exactly tar and not exactly rust but feels like a combination of both. The 700/900 FAQS page includes mention of products called wax & grease removers that are used when repainting. Will one of these products work to clean painted surfaces without eating the paint? And, when hunting for a cleaner/wax & grease remover at an auto parts store, are there ingredients/products I need to avoid when working with paint that's 17 years old?