The gearbox having a vent tube is open to the atmosphere, and going from a hot state during running to a cold state, parked in the trailer or garage, the oil will collect condensation. Also, the oil level plug being very unreliable, I like to drain the oil and refill, so I know I have the proper amount. And, and… how much is a quart the best of the best tranny oil compared to the fuel bill to get you to the track????
I know everybody is on a budget, but to me it’s like asking how often should I brush my teeth? As often as you can….