This is interesting, I'd not heard of this issue before. Is the fix for this a new/used head? Or can the head be repaired if this were to happen? Is there any way to diagnose this short of pulling the head and taking it to a machine shop?. It is a common fail point when a hole will develop and allow oil to drop directly into the exhaust manifold passage of the head, bypassing the cylinder, which would explain why you don't have significant smoke.