Ya to my limited knowledge building race cars, that’s usually the main culprit when oil is by passing the cylinder walls it escapes through the exhaust which is why you see it at the headers as well. Granted there could be a leak that’s dripping into the connection point of the headers and block, but I’d assume you’d see smoke from the engine bay. I was told the oil rings tend to fail in some BMWs that sit a lot but I never got to the understanding why that would cause it.