My 1986 300E has suddenly had a drastic drop in gas mileage. I generally get 18-20 here in Maine during the winter, but I am now getting about 12-14. The car is running fine, no hesitation, starts easily etc. I changed the plugs about 3 months ago, and cleaned the distributor contacts and rotor at the same time. The air/fuel milture was set at taht time too. It almost seems like there may be a fuel leak? If this is NOT the problem, then why the sudden drop in mileage?