Anyone have success on using a High Mileage oil with respect to stopping small oil leaks? GF has a G35 Infinity with 165k that has a small valve cover leak, and the valve covers are a royal pain to get to on this 3.5L V6. Was thinking of using "Valvoline High Mileage with MaxLife" next oil change and see if it helps. Anyone seen a high mileage oil actually help out with something like a slight valve cover leak?