How do I tell if a rear main seal is leaking and how do I fix it on a Chevrolet 250?

Recently my engine began to leak oil from that area and I've checked the oil pan bolt(was tight) and the oil pan bolts and I tightened them all up to snug but it's still leaking. The engine/trans is about to come out anyway so what are your ideas?


1968 Camaro - 250 (No, I'm not gonna drop a 350 in it!....Jeez!)
1968 C-10 with 2 extra cylinders