Hello, our Pin Oak has had this problem for awhile and I can’t find anything on Google about what it is. We cut a small limb in October a few years back and noticed it was black in the core. Now the hole is weeping a black substance. There is also a small hole underneath it that has developed a crack that has worked its way down the trunk. The tree is otherwise healthy. The only thing we can think of is our son use to shoot BB and pellet air soft guns and maybe he shot and penetrated the tree with a copper or lead pellet. Do you have any ideas and is there something we can do to keep this tree. Thank you very much.