There are three drain plugs, the one by the mid PTO shaft and look at the lowest point on both sides of your rear axle/trans housing......they look like all the other bolts that hold the cases together.....but thye are in the centre and if you look real close you will see sealing washers behind them.
Manual and WSM doesn't show their location good at all.
Kubota reps at a dealer show told me you could use either oil in the front axle, but recommended UDT.
They said the complaints you see about axle seals leaking has nothing to do with the oil.
And the front axle is supposed to hold pressure. No need to vent it like you see people trying to do.