Which component is NOT checked for leaks or condition in the engine compartment?

The air filter is not typically checked for leaks or condition during a pre-trip vehicle inspection of the engine compartment. Instead, the air filter's primary function is to clean the air that enters the engine for combustion, and it is generally assessed for its ability to block dirt and debris rather than for leaks.

In the context of a pre-trip inspection, components like the power steering pump, transmission casing, and fuel tank are crucial, as leaks or damage in these areas can lead to serious operational issues and safety risks. The power steering pump could result in steering difficulties if it leaks, while the transmission casing and fuel tank are critical for the proper functioning of the vehicle's transmission system and fuel delivery, respectively. Therefore, focusing on these components ensures the vehicle's safe and efficient operation.