In gearboxes, oil acts as gear and bearings lubricator, moreover it dissipates the heat and brings power where it’s needed (i.e. in paper mill cylinders, the hydraulic oil that’s used to regulate their diameter, once terminated its function, goes outside the regulating valves that are inside the cylinders and flows to the gearboxes that move the cylinders to lubricate them). A wrong oil topping, may say damages difficult to calculate: it’ sufficient to think about a mill plant, it’s breakage may determine the production stop.