Originally Rotella T6 5w-40
VM Motori has said to use a Synthetic European oil, 5W-40, MS-12991. So I am now using Quaker State Euro Full Synthetic 5W-40 (5-Quart - 22.97 Walmart & Amazon) The MS-12991 spec is what's important.
What makes you lean towards Amsoil? Amsoil reports better deposit prevention by a significant margin. I have never heard of premature engine wear or failure when using any of the top synthetic oils, so I wonder, what does better deposit prevention accomplish? The Amsoil fanboys swear by it. I agree it is a great oil, but better?