The oil level in a lubricator is checked ___________ and replenished with ____________?

The correct choice emphasizes the importance of maintaining proper lubrication to ensure optimal operation of machines that use fluid power systems. Checking the oil level according to oil usage means that maintenance is performed based on the actual consumption and performance needs of the system, ensuring that oil levels are adequate to provide lubrication when required.

Replenishing with the recommended oil is crucial, as it often means using oil that meets specific viscosity and performance standards for the application. Many systems require oils that have particular additives to enhance performance or prevent wear, making it important to follow the manufacturer's guidelines.

This choice reflects best practices in fluid power maintenance, focusing on the needs of the system rather than a fixed schedule or a specific type of oil that might not be best suited for the application at hand. Regular checks and using the specified oil help prevent potential failures or inefficiencies that could arise from improper lubrication.