Volkswagen Group of America, Inc. refusing to cover warranty Herndon, Virginia

We leased a new 2010 Jetta that developed engine problems after 8 months.  Volkswagen Group of America is claiming that we used bad gasoline.  We live in Hawaii where all gasoline comes from the same source except that some stations have extra additives they market.  We also have seven cars in our family and all use the same station most of the time.  I asked VW how we can tell if the gas we are pumping is bad and there is no explanation.  VW Group is requesting that we pay for a fuel flush and that we will need to do this every 5000  miles.  Seems like they are having problems with the car and not gas if they already expect us to perform maintenance in the future even if we buy gas somewhere different.  This is a new car with a three year warranty and three year easycare maintenance agreement with only service required at 10,000 mile intervals.  Our car only has 7500 miles currently. We feel that VW Group is trying to avoid the cost of a problem they are having with their vehicles and trying to pass this on to the consumer.  I feel they need to tell me where I should not buy gas at the time of purchase to have a legal stand to not covering this under warranty.  If all the gas in Hawaii is bad in their opinion, they should not sell cars in this state.