Besides the oil level, what might be part of serving the gear box?

Inspecting seals for leaks is a crucial aspect of servicing the gearbox because seals are integral components that help to maintain the integrity of the gearbox. They prevent oil from leaking out and contaminants from entering the gearbox. Over time, seals can wear out, become brittle, or degrade due to exposure to heat, pressure, and lubricants. Regular inspection of these seals allows for early detection of leaks, which, if left unaddressed, can lead to decreased lubrication efficiency, increased wear on internal components, and ultimately, gearbox failure.

In contrast, other options like replacing spark plugs, adjusting gear ratios, or cleaning air intake components are not relevant to gearbox servicing. Replacing spark plugs pertains specifically to an engine's ignition system, adjusting gear ratios generally involves modifications related to performance tuning, and cleaning air intake components is primarily associated with maintaining the engine's air-fuel mixture. These tasks do not directly support the functional integrity of the gearbox. Thus, inspecting seals for leaks is aligned with preventative maintenance ensuring the proper functioning of the gearbox system.