I learned the hard way, always start with mild then go to wild. 409 is a good place to start but there's better mild solvents for removing bugs and tar. I've used a PPG product and generic equivalents for years and they double as a pre-paint cleaner. Here's one from 3M: http://www.autobodytoolmart.com/3m-prep-solvent-70-08983-p-10947.aspx?s_kwcid=TC%7c6058%7c3m+prep+solvent%7c%7cS%7cb%7c7185278345&gclid=CIubl5qwoLYCFcqd4AoddA4Aqg