Can you see where it is leaking? Are you sure it is the rear main? 99% of the time the oil is from the HPOP, HPOP lines, Turbo Pedestal, CC oil out of the intercooler tubes, Exhaust Back Pressure Valve, Valve cover, or maybe even the fill tube... I would drop a hose in the valley and wash it out real good. Then let it dry and then start watching it.