I have from experience come to the conclusion that if on the metro, one side works and operates the blade into beta and negative angle and the other doesnt, it turns to poo very quickly!
Apparently if the NTS fails, and the prop drives the gearbox, its the gearbox which suffers really quite badly... the other consideration is the metro is a shaft drive not a free turbine. Any abnormal activity from the prop, engine and gearbox is bound to be expensive.