What is the current consensus on the best oil for the gearbox on the 575? I have seen recommendations from redline to Motul to Ravenol. It looks like Shell now makes a "Spirax S6" 75w90 GL-5 gear oil; I can't find their (I guess out of production?) S5 oil anywhere. I like Ravenol J1C1109 (75w90 full synthetic) in my TR...was going to lean the same unless consensus leans in another direction. Was planning on 11 bottles aka 11L.