First post here guys. Just wanted to add a little first hand experience if it may be helpful. My company operates a fleet of around 10 OH-58s / 206s. We do adhere religiously to the 2 minute cool downs, but do not spin the blades backwards after shutdown. (Other than perhaps half a revolution just to tie it down) We have been using Mobil Jet 254 for the last 12+ years and haven’t had any coking issues.