On Tue, 29 Mar 2016 09:30:24 -0700 (PDT), trader_4
wrote:

On Tuesday, March 29, 2016 at 10:56:47 AM UTC-4, dadiOH wrote:
trader_4 wrote:
On Monday, March 28, 2016 at 9:23:34 PM UTC-4, wrote:

Maybe pour some of that leveling compound in there.
It has a low enough viscosity that it should go into the gap and it
has pretty good compressive strength.

Or epoxy. Epoxy is thin enough that it will run in and fill a gap
like that.

Epoxy can be of various consistencies. "Thin" epoxy would run in quite a
way, "thick" epoxy not much.

Choose the one like Goldielocks did. But following DPB's post, I tend
to think that more is probably wrong than just the alleged shrinkage,
ie that good chance it rotted down below, in which case the epoxy
won't help.

This just demonstrates the fallacy of "treated" lumber. Virtually all
of it is just washed in the chemical and the treatment is superficial
at best. If you can't buy something that is over "2" (not 0.2) CCA,
you are going to be replacing it if it is in the ground. The only
place to find that will be a marine contractor supply or a place that
supplies utility poles. Typically that will be 2.5 CCA. The home depot
stuff may be safe to eat but it is not going to last long in the
ground in spite of what the label says.
I would replace that post with a 6" 2.5 CCA post. If he is near Ft
Myers, I have a 7' piling he can have for hauling it away.