I'd add in The Doomsday Machine. Without medical tests Spock really had no legal right to relieve Decker.
That's not really a situation of an ethical dilemma for Spock, because Kirk resolved the situation for him. Spock had no legal right to relieve Decker, and he DIDN'T relieve Decker, until Kirk manufactured a quasi-legal imperative for him. When Kirk ordered
Spock to relieve Decker, it took Spock off the hook. Kirk assumed the responsibility. You could call that an ethical dilemma for Kirk, but not for Spock. (Of course Kirk didn't perceive it as a dilemma at all; it was instantly clear to him what the right course of action was.)
Spock's ethical dilemma was earlier, as he tried to stay within the letter of regulations while keeping Decker from getting the ship destroyed. Spock handles that with integrity; but it's Kirk who grasps the nettle.
Kirk's order to Spock is a genius moment of writing, I think. It crystallizes a key difference between Kirk and Spock: why Kirk is in command
, and Spock is the best first officer in the fleet. Kirk assesses the situation correctly, and fabricates a non-existent prerogative to issue an order so Spock can do what needs to be done.