RE: Black goo
My experience is that rubbing alcohol (Isopropal alcohol) even at 90% is not a very effective solvent for petroleum based oils. I use Coleman lantern fuel which is basically naptha, whic h is basically cigarette lighter fluid (Zippo, not Bic butane). But, I do not know if WBU or latex is safe from this. Maybe try a small place and let stand a while. Another product to try is Goof Off. Good luck.
By the way, was the Pennzoil the outdoor 2 stroke oil, and have you had any other problems with it? I use the Pennzoil with Coleman fuel in my G23 with very good results.
Sincerely,
Richard