I had mixed feelings on synthetic and still personally believe it can increase leaks. ** However **, when I observed Mobile 1 synthetic to stop all chain slap on an SL with new tensioners/rails/etc (apparently the tensioner was bleeding down), I may be sold and now have it in the car. The best lubrication, especially when a car is started cold, would seem to offer many benefits towards the long life of the car. After watching a chain break free and nearly destroy the engine on my SL, I'll do just about anything in the car to never hear that chain slap sound again, however slight.