After potting this cherry to stabilize the rotting wood, it grew very well on the bench this year. It also continued to rot under untreated areas covered only by cut paste. Areas treated with PC Petrifier, applied at full strength with a paint brush, did well.
The second section of trunk is rotted out on the back. Last spring, I cleaned up the rot, and applied cut paste (the brown, rubbery-looking layer). By this fall, the rot had continued under the cut paste, aided by ants and termites. Peeling back the paste revealed quite a bit of rot, all the way through the trunk:
The first step was to eradicate the pests, with spray, then a rag soaked with more insecticide was stuffed through the hollow and left to steep for a few hours:
Next, using gouges, as much rotted wood was removed as possible.
Then, the hollow was filled from above and below with epoxy putty. I have used this in quite a few situations with very good success. While it will not harm the tree, I hope the seal is good enough that it won’t continue to rot inside.
After it dried, I continued to carve away the rotted wood above it, that couldn’t be filled with putty, and painted it with several coats of PC Pertifier.
Since it’s still nice and warm (early October), it was pruned back and wired with the hope that some new buds would set for next spring:
Nebari Bonsai 
I agree, PC Petrifier is good stuff. I have never tried the Kwik Wood, but interestingly enough I have a cherry which needs work. Thanks.