We had a similar problem on the 350 we run in our circle track stock car. Thought we had a gasket leak, the lower passenger side of the engine and surrounding area would get really wet. Tighted the oil pan bolts, same thing, pulled the engine and replaced the gasket with good quality one, same thing, told to plug the bolt hole by fuel pump push rod, same thing, argh, kept getting black flagged in the races. Finally got one of the old salt tech guys to look at it. Simple thing, the fuel pump had lost its seal and was pushing oil out the front of the fuel pump. The fan must have been blowing it clean off because it never look like it was leaking from there. Got 2 more races in before overheating and blowing the engine. Getting a 400 ready for next year. (anyone want to talk 400 vs. 350 , just kidding, really don't).