I'm having issues suspicions with the Exmark and other brands that use plastic gas tank. Specifically, my Exmark is an '07 and lately I've been having issues with gasoline flow to the carburetor. I modified my fuel system by changing the fuel line and adding tees along with shut-off valves and a dual parallel filter design. I'm experiencing water in the tanks and what appears a milky looking sludge that keeps plugging the filters and now plugging the carb's idle jet causing engine rpm surging at idle. Since the mower is 12 years old, I wonder if the inside of the gas tanks are starting to deteriorate and causing the milky sludge? Do these have an inner coating that can disintegrate and cause this milky sludge? Since day one, I have only used ethanol-free gas and have added Sta-Bil along with Marvel and other additives to my tanks. I wonder if the inside of the tanks are now breaking down?