Adair, have you ever filled the hole or cavity left from the rot on one? My arakawa maple had a hole it from the top where the branches split, similar to yours, and it exited about and inch or two above the roots. It went all the way through. I managed to repair it. I used to epoxy putty to plug the lower hole, recessed it enough so the bark could roll over it. I filled the cavity with a product called Durham's Rock Hard Putty, available at HD or Lowe's. It is a powder that you mix with water, when it dries it is, well, rock hard. Since it is a liquid you can really get the cavity completely filled. I left a little room at the top to put epoxy on it for the bark to roll. Three years later, the bottom is completely covered with bark, you can't even tell where it was unless you know where to look, and the top is almost completely healed over, about a dime size to go, should be completely healed over this year.
Just a thought.
John