[Marshall V. Daut]

My guess is that the hole's threads are stripped or severely compromised. So, someone simply glued in the bolt, hoping that would stop any leakage, as well as trusting that the safety wire would keep it in place. As already suggested, however, internal pressure probably pushed the bolt out. Try threading a different torque tube bolt in the hole to see if the threads are stripped. If so, that solves the mystery. Another half-assed repair by a previous owner that YOU now have to resolve.
Marshall