Why would there be a substantial oil leak from top rear of the engine?

Thanks. It's a 7.4 litre with so much in the way. I've tried to get an inspection mirror in there to look at the darn thing while running, no luck. There is no water in the oil. Should I just go ahead and remove whatever I need, to get to it?

This video I found should be very helpful: https://youtu.be/8n8YS6t3qn8 Simply copy and paste the link above, watch video. ▪️Note: First MARK everything that is to be removed so 'YOU' know exactly how it needs to go back!!!