Have you checked for pressure arising from your engine's breathing system?

I would clean up all the various hoses and connections - don't just look at them, remove each piece to see if any are clogged with dirt and oil. A tiny hose or elbow might just be your problem.

It would be possible to clean the bottom and rear of your engine with a pressure washer without getting water in any of your electrics - this might find your leak and if not, working on your engine would be a lot easier.

Thinking out of the box - is there a place that you could drill a 1/4 inch hole to check for rear main leakage? - you could always plug the hole.