Anyone using Porsche Classic 20w50 motor oil? If so have you noticed any changes to cooling or oil pressure?

Bump.

It sounds expensive. I have used Castrol 20W 50 for 50 years in all my air cooled machines without incident. The formulation has probably changed, but it works well for me and available at FLAPS

Yes & no. I love the stuff.

I wonder if the oil is really a special formulation (it may actually be) or just re-bottled Castrol?

It has been discussed in depth on the 356 forums, and probably elsewhere. I don't know if anyone ever got to the bottom of their actual formula. The popular opinion seems to be added zinc.

I don't know if you can get to the 356 forum without a membership, so here's an oil analysis post elsewhere.

I used Castrol GTX 20w50 for years and years, but I was having a lot of issues with foam on my filler cap. It's said that will happen if you don't drive enough to get the oil hot enough to evaporate the water out of it, but I drive about 25 miles to and another 25 from work every weekday and it was still an issue. Thermostat and cooling flaps are working.

I've switched to Valvoline racing high zinc 20w50 and it seems better. Both are available at my flaps.

Edit, I checked it out, and it's not synthetic. Also it does mention vaguely some engineering done to minimize condensation, and also "high alkaline reserve" to neutralize acidification caused by "aggressive combustion residues".

Where would one buy this stuff? Mail order?

I was looking here. Cool old school-looking metal cans. $$ if that is a quart.
https://www.suncoastparts.com/product/SKU20W50OIL.html

It looks like Pelican has it in a larger size. Not sure exactly if it's apples to apples, but at $60 if that's a 5 qt size, it's about double what you'd pay for Castrol or Valvoline