Wow nice reading the extensive experience you have with these engines & WMO. Yeah it's been a great learning experience, the ring-sticking issues seems to be the last of them, after having dialed in pretty much everything else (filtration etc etc) haha.
I boroscoped the cylinders and they look pretty decent actually, so I was wondering if just cleaning out the gunk in the scrape rings would solve everything.
For example: some Toyotas had a design defect around that ring and burned lots of oil due to it;
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Reading through the comments makes me quite hopeful. Not vouching for that product (yet), but Ill try that B12 treatment on half of the cylinders before I engine swap, then once scrap the engine I'll take it apart and compare the treated cylinders with the untreated ones.
Looking forward to your updates! Enjoy & bless!
Edit:
Similar issue as this person although it isn't as drastic:
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(He did a re-ring and hone)