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If I am annoying you guys by being here and requesting assistance on trying to keep my Connie alive then I would apologise. It was not my intention. I just don't have any other means.
We look at it as a challenge
If you have one of the correct O-rings... They should be a standard metric O-ring, get more. Am sure you have a generic/industrial parts supplier in RSA. And/or, get several with an approximate diameter, and various thicknesses. (thickness is probably the most important criteria). Lightly grease the ring, install it and the sump. Remove the sump carefully and look at the smear of grease on the mating surfaces to see if you have the right thickness.
If you have a means of measuring depth of both recesses (depth micrometer, dial caliper, etc.) you can come pretty close to guessing the thickness of the O-ring. Allow for crush.
As to your cam chain, it looks fine. The 'teeth' (chain and gear) generally ride on a flank of the teeth, and are *not* fully meshed. It's similar for two gears, but visually it's not that obvious.
And per Man of Blues, a slight smear of sealant on the half-moons is all that's needed. I don't have any on mine, and get a microscopic weep of oil... if any at all. +170k miles on my bike.
Rick