Castrol has this amazing stuff. It is in a green bottle, says 100,000+ mile formula, or something to that extent. It has quieted my valvetrain clicking and where my car used to use 2qts per 3k miles, now uses under 1/2qt each 3k. It has also taken a smokey mitsubishi engine, and in two oilchanges fixed it completely, no more smoke. I personally would give that stuff a shot. I also run 20w50, the best stuff ever.