Badly Damaged Bonsai Oak Tree Trunk

[WWB-Walter]

Badly Damaged Oak Tree Trunk
Two oaks - one young, one rescued from demolition site 7 yrs ago (see pics)
Rescued oak was originally found in the dirt pile of a home demolition - looked dead and had lower trunk damage from bulldozer. Tree was originally about 6 ft tall and had grown through dense junipers. Over a three yr stretch, I lowered the tree to current trunk height of about a foot with current growth (spring 2020) after four years in bonsai container.
The up-facing part of the trunk is decaying (from original damage) and very pulpy - a yr ago, pruning wax was applied. This spring, the remaining bark of the upper trunk peeled off, exposing pulpy trunk as well. Fresh growth is 'fed' through bark and trunk on the 'down-facing' part of the trunk.
QUESTION
How to save and maintain this unique, rescued Oak Tree???
Suggestions, Comments would be most welcome. Thanks, WWB

 

[amcoffeegirl]

I am not sure how to save it but I did see this today.

I thought it was a nice example.

 

[WWB-Walter]

2019 - 1 yr ago - Twin Oaks - one with damaged trunk
Just another view of same Damaged Oak with full foliage

 

[Crawforde]

It looks happy, I’m not sure you need to do anything. The dead parts will rot and the live parts will get on with life.
In the future it will be able to tell the little oaks “see this, back in 2012 I tried to take on one of those loud yellow things. I was Lucky to live through that. Don’t be stupid kid”

 

[Shibui]

Just carve out all the soft inner wood. It's probably too late to save it and there's no problem with hollow trunks. In fact I think that can give a bonsai some real interest.
When you have removed as much soft wood as possible treat the remainder with a wood preservative. I use lime sulphur but there's a lot of talk that Earl's Wood Hardener is good too.
Interior wood rotting does not usually harm a tree. The live outer parts will continue to grow and can prevent the rot from getting to the live parts. There are many old trees in forests around the world that are completely hollow and have lived that way for years.

 

[WWB-Walter]

I appreciate those relevant suggestions - all makes sense. Thanks.