Friend of mine just purchased a 95 Cadillac with the Northstar 32V engine. Car is in excellent shape, I think the previous owner did 3K OCIs, no idea what oil they used... I mentioned that an AutoRx treatment using cheap oil and SuperTech filters, then running Amsoil for 8-10K runs would provide long life without needing to rely on 3K OCIs. He's heard of Amsoil before and really wants to use it and would love to free himself from the 3K OCI, too. What viscosity should we use for this vehicle? He travels mostly 20+ mile trips to/from work. Some are long distance hauls. How does that all sound?