LS1 Rear Main Seal leaking.

[lux]

1972 C10 with a LS1 and a 4L60e transmission, I believe the rear main seal and or the seal plate are leaking. Any advise on being sure this is the problem would be helpful.
Has anyone done this repair in the driveway/ garage? How difficult and any advise at all?
It only leaks about a half dollar size spot after driving. I've inspected the top of the engine well and my mechanic replaced the valve cover gaskets, but the problem is still there. The small amount of oil is alway on the back bottom of the engine and on the transmission, defiantly not transmission fluid. It could be the back of the oil pan but, I think it's more than that.

Thanks