I haven't tried Fuchs, but I have indeed tried Castrol. I phoned their technical number on and a lady who clearly didn't have a clue managed to find a contact number for the local distributor in Olifantsfontein. I phoned them, and they had never heard about it, let alone ever sold it!. They came back and said that their local says person will give me a ring on Tuesday.
But, again, the most expensive brands say they are Mercon and Dexron III compatible, which sounds like mumbo jumbo to me.