Maples,that I have delt with I find in discovery die from with in. You may have only a couple of inches of solid material on the outside and the inside totally rotted. I have noticed black ants being a companion along with this. Not saying they are the creator of the problem, also weaping can be seen on the outside. You mentioned a wound, and that also is a sign that it's in trouble. 'Acer species'-Maples have problems with verticillium wilt.