ransley wrote:

Moisture could not be trapped - this is a vertical surface we're
talking about - roughly a circle about 3" diameter.

what insect makes a hole 3"

The exposed inner heart-wood of the tree has a circular profile and is
3" in diameter, and it oriented vertically with respect to the ground.
This is where a secondary trunk had been, which was cut maybe 2 or 3
years ago.

This circular area was sprayed with pruning paint last year. The
surface was solid and intact at that time. The bark is growing nicely
around the perimiter of this area (this is a silver maple). I have two
such similar cuts on a sugar maple - the exposed area was even larger (4
or 5") and painted them soon after the cut was made. This was about 5
years ago. They are 75% covered over now by the growing bark, and they
remained solid (no rot, holes, fissures developing in them).

Getting back to the silver maple, at some point this year I noticed the
appearance of some cracks or voids on the cut surface along with what
looked like sawdust shavings around the crack. Yesterday I shoved the
plastic dispensing nozzle of a tube of PL Premium deep into the main
crack (it went in all the way - I wasn't expecting that) and I pumped
the crack full of glue.