Someone may have overtightened the drain plug. It's got tapered threads and could crack the case if overtightened. It may be possible to stop drill the crack and braze it shut. Or maybe seal it up with JB Weld. To do that you'd need to completely disassemble it and clean it, but the best bet would be to replace the transmission. Might be a little difficult to come by in Austrailia.
If you can, clean the outside of the transmission with brake clean and take a photo, so we can see how serious it might be.
