Yeah, thanks for the insights. I got past the issue and this battery is fresh. My GC is back to normal until the next thing in this, my 17 y/o toy. I did some good old fashioned grunt-work under the dash and fixed a few tired old things.
I'm glad you mentioned low voltage though and I thank you for the kick in my complacency. It was high on my list for a minute as the battery in my Legacy is original from 2010, but then I looked away. I load tested the system, monitored good voltages under load and was happy with the numbers, but still, it's time for a new battery and I'm open to suggestions. There is history of an intermittent main 120A fuse too, which does cause a degree of nagging doubt for the alternator. It only goes to show that keeping these whips past their prime, about 6 years by my estimation, is not for the faint of heart unless you can be your own tech.