I owned a 65 VW which I bought new. I changed the oil every 2,000 miles using SAE 30 and did a valve job around 40,000 miles to guard against the #3 exhaust valve failure. I did a complete rebuild around 75,000 miles and at that time the rod bearings were showing copper so they were worn out. If I remember correctly, VW put a 2 degree spark retard on the #3 cylinder to drop the combustion temperature a bit to hopefully keep the valve from failing as fast.