The gunk is a known problem that comes from certain supplies of E85. We don't see that here in AZ. There are various theories like old fuel tanks in gas stations supplying E85 or whatever. I've never seen it tracked down to a known cause.
2015 F150 4x4 3.5 Ecoboost
2002 Camaro SS, new turbo install in progress...
2005 Neon SRT-4, Big wheel stage 3, E85