When oil turns milky, it's because of water contamination. Was the oil leaking from the rear shock, or the vent tube from the engine ? If it is from the vent tube, I sugest draining the transmission oil. If it comes out milky, then you have a worn water pump seal and possibly the bearings and the water pump shaft as well. If it's coming from the rear shock, this is very rare, infact I have never heard of such a thing, but you will probably have to get the rear shock re-built.