The Costco near us only had 10-30W Mobil 1. Manual calls for 5-30W. Forget the 10-30 and stick to 5-30W? (This month, one of the local auto parts stores -- Advance -- has a "Mobil 1 oil change special" listed for $29.88. "Buy 5 Quarts of MOBIL 1 Synthetic Motor Oil, High Mileage Synthetic or Extended Performance Synthetic AND a MOBIL 1 Oil Filter.") Any experience with Mobil 1 filters? Our V8 has 36,500 miles.