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I work in a clean room engine production facility and I've fitted rustier parts than those to brand spanking new engines

To me it just looks like a bit of superficial surface rust on some not-very-important bolts?

I’ve had first hand experience of Arnold Clarke and will never never buy a car from them again.

Yeah sorry there's nothing wrong with that at all, it's just a bit of minor surface corrosion as others have said. On the bright side I really wouldn't worry about it, the car is sound so if your son is enjoying it, then tell him the good news - it's fine, it's safe so go enjoy it!