Motor mount failure has been known to happen from time to time. That could very well be the cause of this "leak". Have you noticed any "natural gas" type smells while driving? If the PTU vent is puking, it is pretty obvious. With regards to seals, the PTU-transmission seal is the one that leaks, and the mix comes out brownish pink (trans + PTU fluid), but that should originate on the other side of the PTU, not the passenger halfshaft side.
So I'd clean up the area for now and watch more closely to identify the real source.