Gearbox flushing is critical because it removes residual worn particles, water, oxidation products, and other contaminants that standard draining cannot eliminate. During this process, flushing oil is pumped at pressure (up to 5 bar and heights up to 105 m) through internal gearbox channels to displace old contaminants. This helps prevent contamination of the new oil, ensuring the longevity and performance of the drivetrain.