I used Royal Purple Max Cycle in my '71 Super until the day it died.
I will be using Porsche Classic 20w50 when it becomes available in my '74 Thing.
Porsche's release
I'm sure folks will poo-poo the necessity and others will jeer the probable cost, but I respect Porsche for still recognizing
and supporting its air-cooled past. In the end, oil changes are the best and cheapest insurance one can buy.
(While VW doesn't address its air-cooled past except for stray t-shirt or key chain in Driver Gear, they do recommend all sorts of different engine oil for their different engines, so I believe in mating the right product with the right product.)