SAF-XO vs. Syntrax.
Hi all!
Just so everyone's on the same page, Castrol SAF-XO and Castrol Syntrax Long-life 75W-90 are exactly the same fluid. There has been no change in fluid specification - only the name has changed.
It's a fully-synthetic 75W-90 GL-5 (i.e. extreme-pressure rating for hypoid bevel gearing) fluid. Basically the same stuff you'd get in the rear axle of a common-or-garden HGV - expect much, much higher-quality.
It needs to be that good to cope with the heat and pressure BMW Motorrad compact final drives are capable of handing out. You could use ordinary GL-5 fluid if you wanted to, but it would break down into sludge very quickly.
One other thing: I've known some BMW service desks (especially car service desks) to try and sell customers SAF-XJ when they can't find SAF-XO on their shelves. BEWARE! It is not the same thing - SAF-XJ is a 75W-140 oil designed for limited-slip differentials.
Very occcasionally, and depending which dealers you're in contact with, you might also run across SAF-XA. This is an 80W-140 oil, also designed for limited-slip differentials.