What other indication suggests the AMAD needs servicing apart from the sight glass?

The correct answer highlights that MSP codes 982 and 983 specifically indicate issues related to the AMAD (AUXILIARY MULTIPURPOSE ADAPTER DRIVE) that require servicing. These codes are diagnostic messages generated by the aircraft's maintenance system that directly point to problems within the AMAD system. The presence of these codes serves as a clear and reliable indication that action is needed beyond just a visual inspection, as they are based on quantitative data collected from the system's performance and health.

In this context, the other options do not provide direct evidence of AMAD servicing needs. While visual inspections, engine performance issues, and low hydraulic pressure alarms may suggest related problems, they do not specifically indicate that the AMAD itself requires servicing. Therefore, the MSP codes are the most definitive sign of the need for maintenance in this case.