Well here's an update from using the sonicator mentioned in that 6mmbr article. I don't know if it's because my brass was fired up to 1.5 years ago, but 24 minutes in full vinegar with soap didn't do much for primer pocket dirt, but it did clean up most of the dirt on the inside walls of the case. Same result with full strength lemon juice and soap. Therefore, I decided to break out some bigger guns. I ended up cleaning 100 out of my roughly 800 once fired cases.
What I Did:
I have some nice plastic containers that pretty much fit the whole sonicating tub, so I used it for all the cleaning. Cleaning solution was about 300 mL total, which gave a nice covering to each batch of 25 .223 cases. I swirled and tilted the solution around to make sure it got inside all the cases.
In terms of solutions, I used 24 minutes in 1:1 noname CLR, vinegar, with a touch of soap, 8 minutes in vinegar with soap, 8 minutes in water with baking soda (more doesn't hurt, baking soda is a very mild base), 8 minutes in water, and then dried them with a heat gun. I used the high heat setting, holding each case with metal tweezers and blowing ~ 6 seconds into the mouth of the case and 3 seconds on the primer pocket.
The 1:1 CLR, vinegar and the vinegar solutions can be reused for up to three batches, which is good since each 150 mL of CLR is like $1.50. Everything else is relatively cheap.
Thoughts:
The brass is quite clean, with a tiny bit of dirt visible only on the odd case here and there. Maybe shifting the brass around after every of the three initial sonications will take care of this problem.
There are just a few cases that have either a) a medium sized patina type discoloration, or b) a small brown almost rust-looking discoloration, but I can't feel any depression with my nails. Is this worth worrying about?
I'm not happy I had to use stronger acidic conditions, even though it's hard to know exactly how acidic it was using pH paper, and also the effect on the metal depends on the specific acid (look up aqua regia for an example).