It's unlikely that it leaks from the head ( not because there is no oil in the middle either ) , the oil leaking from the cam seals and the rocker cover will travel down and until you fix that you won't know for sure .
Yes you will have to remove the plenum to remove the head but if i was to remove the head , i would prefer to remove the engine out , or at least lift it up a little to get to the plumbing under the plenum easier and get to the turbos easier too.
Once you remove the plenum its very easy to remove the cil head .
if you have good compression do a leak down test as well and if thats very low i would take it the engine is in good nick so i would replace the seals , half moons at the rear and new rocker cover gaskets and put it back together .
How come you removed the plenum twice ? What a job to bust your knuckles , no skin left after that i bet .