OK everyone. So I'd procrastinated long enough and finally decided to try using StarSan as I've seen suggested many times searching around. I used 4x the concentration of the usual used for sanitizing. So, I used 2oz StarSan in 2.5G of water. I rolled the solution up around the kettle walls a couple of times to coat them and then I let it soak for about 30 minutes, no longer. I could see even after a few minutes the solution taking on the color of the beerstone. After about 15-20 minutes I took a regular dishwashing scrub sponge and used the scrub end to rub one area of the kettle wall and it came right off and onto the sponge. So after 30 minutes I dumped it out, then did my usual oxiclean free sponge scrub and it all came right off. Here's the clean picture. Kicking myself for not doing this sooner! LOL.