Hi, I have been running Valvoline Synpower 5w30 Dexos1 in a GM 3.6 LFX. At the moment, I have access to Castrol Edge 5w30 Long Life which is a VW504/507 acea c3 low saps oil. I can get the Castrol at half the price of the Valvoline, so obviously tempted. My concern is TBN retention using high sulfur ethanol fuels for 15,000klms (roughly 9500 mile) intervals. Any opinions on running VW 504/507 in an engine designed for dexos1 operating with high sulfur ethanol fuels (as well as how you think 504.507 would go in this engine) would be appreciated. Thank you