Yes, exactly. Hopefully that's what Yesfan meant to say. But this is definitely the case.
(or the disconnect, etc. but not the dip tube or its o-ring)
Nope, I thought it was the diptube o-ring when I last posted. Thanks for the clarification. This is good news if you guys think it's the gas post o-ring. Should be a simple fix.
I bought a bunch of orings for my dip tubes and post back when I started brewing. Someone here posted the Oring sizes from McMaster Carr for kegs, so I bought a bunch of spares. I'll swap the gas post out.

The keg hasn't lost pressure since my last post. In fact, it may have gained 1psi since then. Worst case scenario is for me to remember to unplug the disconnect if there's still a leak if nothing improves.
You all don't know how much I appreciate your help and patience in all this. Wish me luck.