Reading through your post and thinking of it from a mechanical aspect.
Engine leaking, happens, odd it was dry for a couple weeks and then let go though. Maybe a pcv was blocked and pressure pushed out there.
Engine blowing, it is a 3100. Likely the intake gaskets were not done often enough or replaced with the aluminum version that is now available. Something to consider on your new engine. Intake gaskets are common on the 3100 until you get the aluminum framed ones in there. Honestly though..I doubt the guy knew anything about the motor about to blow. That's not something you can hide.
Transmission being full of fuel. I don't understand how it's possible unless someone poured it in there intentionally. Even then.. the temps our transmissions see, a lot of that fuel should have evaporated and been causing serious issues all through out the trans. I don't understand how a trans can work that way.
