Are you going to replace the squared-off looking o-rings on the barrel there and inside the barrel bore? And all the other ones as well? They look a bit old. If I were going to the trouble I'd try and find some replacements made from Viton. Also, carb cleaner is bad for o-rings,especially if they are plain old nitrile and not Viton. It's hard for me to understand how that one is junk. Looks like a new one.
But good on you for doing this exploratory work. I was always under the impression these were not rebuildable. My fingers are crossed for you.

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