By all objective measures, synthetic is better. That is undisputed. So, Tom, why ya on the fence?
Don't you want the best for your just-barely-broken-in 500E? Don't think you need the extra measure of heat capacity? Don't like the increased lubricity? Don't like the fact that it won't coke when it gets near them wicked hot pistons? Just do it, compadre-these motors are HOT, and in time will destroy repeated helpings of Dino oil, a tiny bit at a time
