Change it often! Not yearly, you go to track, dump it, youre a heathen in NC hooning all day at 9k rpm, change it. You baby it, change it often its a rocket.
OK, then.... I use a proprietary blend of used fryer oil (from the tank behind KFC) and used car motor oil from the recycle center. 50/50 ratio. Shifts are buttery smooth and finger lick'n good!