pilots are generally trained to make a mayday call to declare an emergency, if only to make the point that they do not want to be messed around
Well then they've been trained incorrectly.
A emergency, or a problem such as this, is a PAN, a MAYDAY is supposed to be only used when a loss of life is imminent, as a recent example the Swiss B777 in to Frobisher made a PAN call when they found themselves reduced to one engine.