I drove my 1985 Honda Civic on nothing but 10w40 back in the day for 120,000 miles. Under that valve cover it was spotless. And thats living in the torturous northeast conditions its entire life. That was using dino oil as well back then with 3-4k OCI's. The body rusted off that car before the motor ever died. I think alot of it depended on engine design back then.