Yes some of the newer GM vehicles are supposed to be E85 ready and Viton does not like Ethanol.
It would be nice to know for sure what elastomer O-rings were used in our fuel system.
For example what are the o-rings made from on the AC Delco injector kit # 317-454.
They are probably made from one of these = Buna-N, Viton®, Neoprene.
It would be nice but unlikely that GM will use many of these $10.00 and up o-rings. = Viton ETP (Viton Extreme), Chemiz, Simraz, Kalrez.