This was one doleful, miserable, dirty-as-a-nightsoil collector job.
I should have been able to just replace the $.23 crush washer. But the PO, as all Porsche owners know is super dangerous, stripped the threads and super tightened the OPRV. The result is that I had to replace the cooler housing and all associated gaskets.
I followed the Clark's garage procedure. With just a couple of modifications.
First, I did not loosen the exhaust manifold. Maybe I have small hands but I was able to get to the bolts I needed to easily.
The second thing that I did differently was that I put the gasket on the assembled cooler and housing, not on the engine block. It was much easier to tack the gasket to the housing with some Loctite 574.
This allowed me to be sure that the gasket was aligned.
And regarding the alignment tool. I asked to borrow my mechanic's tool and he said they never had one. Never needed it. Replaced over 100 of them in 944s and saw no need. I had no problem doing without. It fired up and worked fine.
The joy of owning a car that for now is not leaking is off the scale.