The correct answer is C) Notify the watch or duty engineer immediately. This is the correct answer because the presence of a significant amount of oil discharge when blowing down the scavenging air receiver drains indicates a potential machinery malfunction or failure that requires immediate attention. As an expert on the operation of the propulsion system, you have an obligation to report this issue to the responsible personnel, in this case, the watch or duty engineer, without delay. Timely notification allows for prompt investigation and corrective action to be taken, which is crucial for maintaining the safe and proper functioning of the vessel's machinery. The other answer options are incorrect because they do not address the need for immediate notification. Waiting until the next work period or the next time the chief or first assistant engineer is seen could allow the problem to worsen, potentially leading to further damage or even a safety hazard.