"...the one I'm familiar with is silent on the subject. Which clause is it that forbids service with the United Nations..."
Which clause permits it ??
Let's face it, other than you loathing for the United Nations, which I won't say I disagree with totally, you have no grounds for saying that New violated his oath. New doesn't have any, either. So deal with it. He took his shot, made his stand, stood up for what be believed in, and paid the price when others determined he was wrong. He doesn't have to accept the decision but he might as well grow up and live with it because, well, because he was wrong.