If your Daihatsu Feroza / Daihatsu Rocky / Daihatsu Sportrak is leaking gear oil ("40 weight") one of the things you might want to check for is if the yolks on the propeller shafts are ok.  While it isn't too common, it also isn't too rare for the seal to fail on them.  Mine failed because the bolts holding the transfer case to the mount on the cross member fell out.  The extra movement of the transmission and transfer case caused a hydraulic pressure that broke the seal.

Below is an example of a bad yolk seal on a front propeller shaft.

The solution is to either (1) purchase a new yolk or (2) weld an oil tight bead all the way around the circular seal.  To do this you must remove the propeller shaft.  For instructions read the section 'Propeller Shafts' in the Daihatsu Service Manuals.