fuel soaked balsa
I have used a spot remover called K2R on the advise of several people on this site. I picked mine up at the local grocery store (Publix). I have looked at WalMart, Kmart and others to no avail.
All you do is spray it on, let it dry and wipe it off. You may have to repeat this a few times depending on how much you need to remove. Hope this helps you out.