Grn, you've got nothing to do, paint a link and a tooth. Count how many times the chain comes around? I forget if it was 65 times to get to the realignment marks to line back up, but do you now see a wear pattern every 65 revolutions on the same plain? Link over one tooth, she now wears in a new 65 times around is the wear that was in a groove sort of.
Key that link, you have this wear spot that might turn high spot. Ever hear that wahhh-wahhh coming down the road all hi/low chiming in; that added wear? If you lost o-ring, you could have pushed grease up in there, saved yourself a whole bunch of parts and time having someone doing it.
I was the only idiot in the shop key'inn your chain to sprocket so you couldn't wahhh-wahhh me, I worked on your bike, now point a finger?