Quattro owners: My 93 S4 has been gettling lower milage (2-3 less miles per gallon) over the last few months. Several people have told me that was due to "oxygenated fuel" which is prevalent in California. First of all, is this a valid argument ? If true, does anyone know of any gasolene companies that do not "oxygenate" their Premium Unleaded ? Thanks a lot. Joe Petersack