I have a 23 year old red maple tree. About 15 years ago, one of it's limbs broke off, due to heavy winds.. I sealed it with pruning spray, and in time the surrounding bark healed. This year, the tree has developed a soft spot where the limb broke off years ago. I put my hand into this cavity and it is filled with mushy tree fibers. Is there anything I can do to save this beautiful tree? Should I clean out the mushy fibers, seal the wound and fill in the hole with a non toxic tar like material? If so, what would you recommend I use. Thank You, Ted R. King. See attached images