Ok, making more progress in my research. It appears to be an external head bolt that is prone to breaking on earlier model engines. Other sites say it may/may not leak oil. Also finding various answers that it could be a simple fix, or could require replacement of all head bolts. BTW. My thoughts are the vehicle is dead-lined until the bolt is replaced. I would suspect a chance of warping the head if I continue to operate the vehicle without the bolt. Any thoughts?