[Rumnarv]

Check to see if your drain plug is tight, could be blowing onto the center support while driving. Can you see if it is comming out between the tranny and engine (rear main leak? ? ?). If it is not leaking there check the back of the heads for the camshaft end bushing seal. You will probably need a mirror as it is very close to the firewall. See Pic below

 

[Rumnarv]

Check the back of both heads same place (you said head, so I don't know if you only looked at one.).

Yeah the tranny is a biach to pull w/ engine in car. I would almost rather pull the engine tranny as an assy.

Hope you get it figured out...