i have the same problem, and its been there for about a year.

but, not from gas. I had a can of Arizona sweet tea, and poured the last inch or so out the window on a hot day, not really thinking anything of it. a few days later after a wash it was still there. and still is after several scrubs/products. its about the size of a baseball but not as dark as the gas stain. but still very noticable. grrr