Yes, I have thought about the possibility that a plug let loose.
I just figured that if that happened, it would be MUCH worse than it is (as bad as it is.)

But there is no external leak anywhere. Definitely not the valve covers or oil pressure sending units. The oil is pouring out from between bellhousing and bellhousing cover. So the leak is definitely coming from the back of the engine, inside the area covered by the bellhousing.

I haven't crawled underneath and pulled the cover off. I just put the car right back in the garage because I am just so disappointed with the thing right now.