I've race my current S/P car using local pump E85 for over six years with no oil problems using Valvoline 5W20WT for three years and then I switch to VR1 10W30WT the last 3 years
I swap motors last winter and continued to use the VR1 10x30 wt. oil, I changed it and filter once due to being a new motor and I wanted to see the oil and filter contents, the oil look really good and I haven't cut the oil filter apart yet
BTW, I don't like or use synthetic oils if I don't have to