First get some high quality yellow wood glue, mix some glue with water to make it about the constancy of milk. Put it in a spray bottle and spray it on the bad wood. If the wood is dry it will soak it up fast done correctly it will restore the strength to the wood, if you have chunks missing mix sawdust and the yellow glue to a thinned putty consistency. Make sure the area you are using the putty on has been sprayed down with the solution above. Fill in your hole and smooth it out as best you can. I will become extremely hard. You can even drill holes in it for mounting purposes. I have created test pieces and was able to break the board before the joint.