Your cam shaft plug was backwards? Must have been a Chevy man who put it together
Let me guess concave instead of convex installation. I hope it is not my cam plug or any other plug. That would mean pulling the tranny and bell housing. The leak is coming from the lower part of the shaft on the back of the block, at least that is the way it looks when viewed with the inspection cover off. Oh, by the way, what is the torque spec for the rear main cap when I re-install it?
--Mike