High pressure oil lines going into the block? I chased this ghost for months and ironically showed up after valve cover change and on DS. First time was the valve covers not being seated then replaced and still leaking mind you not as bad as yours but enough to see it.

Did the same as you and pulled out handy mirrors and sure enough the bugger was leaking at block the o ring was bad. Now mine is a 4.6 so just giving you another option.