Japanese Maple Trunk Rot-To fill or not to fill

[Thanasi]

Hi, I have had this tree or quite a long time. It's one that I have neglected and not one that I never thought had a bright future because of its twin trunk that starts higher than I would have liked it to start. I have used it in the past to propagate new trees from higher branches. However, my problem with it now, is that I had never sealed the wounds and I have created rot. As you can see in one of the branches the rot is open in the node and also the trunk is completely rotted. The rot goes all the way through the trunk into the soil. Otherwise the tree is completely healthy.

I have a few questions,
1) do I carve the trunk open, clean the rot and seal it back with putty. Have used Durham's rock hard putty on another tree but not sure if that was the right thing to do. Some say let nature take its course with rot, other say clean and fill in all rot.
2) do I do the same with the higher branch (the one on the right in the ist pic). Clean it and fill it in
3) do I cut one of the trunks (the one the left in the ist pic) , open the other trunk a little by grinding the rot and make it a single branch tree
4) and finally, is there a possibility that this tree could look any better if I thread grafted and grafted seedlings to the existing roots to make a better looking tree

Thank you

 

[Shibui]

Rot in a trunk is not a death sentence for most trees. The centre heartwood is essentially dead and does little for the tree so we see many venerable and famous trees that are completely hollow inside and are still healthy and viable.
Hollows in deciduous trees seem to be traditionally frowned on but that seems to be changing slowly. I'm quite happy to make a feature of hollow trunks, even with JM provided it appears natural and appropriate. The final decision will be up to you as the owner. You need to be comfortable when viewing the tree.
The tree cannot grow over holes. Filling the hollow may allow the tree to grow over but that will still take some years.

I agree with your assessment of the awkward double trunk starting high. It is always very hard to work out a good design just from looking at 2D pics. Cannot really geta feel for where each branch starts and directions so any virtual advice needs to be tempered with what you see in reality.
As always there are many possible solutions and here's just a couple of possibilities I can see in those pics.

Layer under the main fork for a traditional twin trunk. Not sure that's a viable solution here as both trunks appear almost equal in size and the trunk bends and direction do not appear harmonious.

The best option I can see is pic 2 above with the left trunk removed but leaving the smaller branch there as a first branch, tilt the trunk a little left to re-balance the visual weight for informal upright and see what happens. Note there are always some risks. Removing large trunks is not always straightforward and a chop like that will take a long time to heal at the tree's current age and health.
Your tree has way too many branches emerging close together. It is common with JM but reverse taper develops quickly and may even increase as cuts heal after pruning excess branches.

Not every tree has the potential to be an award winning bonsai. Sometimes it is quicker and better to start over. Assess each tree based on merit, potential and problems to be overcome and don't let sentiment get in the way of producing good bonsai.