ThanksI can’t guarantee that the Australian version is the same, but very likely this operators manual will help :
https://www.kubota.com.au/wp-content/uploads/2015/09/agopszg32701.pdf
Your transmission looks identical to mine on ZD326 / 331.
Large center drain bolt, 2 axle drain bolts (if no fluid comes out try the one not fitting the pattern around the housing).
My mowers will only take 8 quarts on refill, then start the machine, gently move forward and backwards a few times. Add remaining fluid.