oil pan or rear seal

[jolobo64]

64 c 10 350 chevy small block ( mid 70's engine), I have checked all obvious areas for oil leak and I am sure its at the rear main seal or oil pan. Just not sure which one from the two. I had the rear main seal replaced before but maybe the guy didn't do it right or maybe he didn't seal the oil pan back right.

This time Ill do it myself, I have not dropped the pan yet but there is wet (oil) right at the front lip (curve) of the oil pan.I know either way it goes I have to drop the pan but I don't want to replace the rear main if no need and I also am trying not to just do the oil pan gasket and then see if it works and if good , good but if not then I have to drop it again and do them both.

Just wondering if there is a way to tell clearly between the two when I finally drop the pan.