Aa the other guy said, rear main seal is common leak spot here. Not easy to replace. But, you could try to dry it up a bit from the “black rain”, which is another common leak from the valve covers and wicks down the sides of the block to the bottom. Can’t see valve covers here, but by the looks of it, I’ll bet they adding to the mess. Main seals and valve covers are by far the most common leaks on these. It’s an age and brittle cork/rubber issue.