As Richard says it is the bits MMC added. On your car keep an eye on the pipes around the tank and the fuel filler.
My 2014 Roadster seems fine but here in the UK you can still get E5 and the local Esso garages E5 is no now ethanol free.
You may get more issues with your lwan mower & other power tools. Plus using an additive like Sta- bil fuel stabiliser can stop / slow down the fuel absorbing moisture.
