Have You Cleaned off the Engine? to reinspect the source?
Yes the Early c2 c4 had Major problems with loose heads
and The dealer was Installing New Pistons and Cylinders and Cutting the surface of the heads...also the Case Bolts leaked a lot
and The Surface between the cam housing and the heads leak
Dont forget the oil return tubes...They make a Split oil return tube for that..easy to install..I Have done Lots of them!

First source out the oil leak ..Then attack


Also YOU said bank 1/3 front..Inspect the Rocker shafts..
I Have seen Several left loose and they WILL be hard to diag !

I Would clean the engine and add dye then reinspect for the leak

I Can Recommend a Great Porsche Only Machine Shop in So cal Ollies Machine in Santa ana...They do all of Andials work..The Best!