Year model? Mixing the oil will not cause this. Ethanol. That black sand is deteriorating fuel line and really plugs up fuel filters, manual fuel pump, the fuel pressure regulator on these motors. Gets bad enough it will cause injectors to stick.
The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD