[Henry Schmidt]

The topic is sealing a Porsche engine case and what works. Not what might work....

To that end I'll state unequivocally that for over 35 years I have produce high quality Porsche engines.
Over the years, when appropriate we update our process. We even develop new products when a suitable product is not available.
15 or so years ago we were introduced to Mil Spec Dow 55 o-ring lubricant.
We began using it (Dow55) on low hour race engines to test it's suitability.
After a few hundred race hours on multiple engines, tearing down when hours dictated, we became satisfied that the product preserved the o-ring fit and flexibility better than dry, plain oil, synthetic oil and silicone grease.
After that we started assembling every engine (200+) using Dow55.
No leaks attributed to o-ring deterioration were ever observed.
No leaks attributed to o-ring deterioration was ever reported.

As soon as someone comes up with the same or similar data, I'll change our process.

There are a plethora of proven techniques and even more theories in this thread.
My goal has always been "to help the novice with advise to aid in a successful rebuild". I don't own Dow stock, I don't sell Dow 55 separately (I include it for free in our kit). If you're unsure of this or any other technique I share, you are certainly welcome to ignore it and go with the advise of a "one timer".