2001-2002 Yamaha 50HP F50Z/T50Z Ouboard 4-stroke engines service manual, Page 89Get this manual
Periodic checks and adjustments
The gear oil level should be at the brim of the check holeRemove the reservoir capand then check the fluid level in the reservoirIf necessary, add sufficient gear oil of the recommended type to the correct level
Recommended gear oil: GEAR CASE LUBE (USA) or Hypoid gear oil SAE: 90
The fluid level should be at the brim of the filler hole4Install the check screw, and then tighten it to the specified torqueIf necessary, add sufficient fluid of the recommended type to the correct level
ICheck screw: Nm (0.7 kgfm, 5.1 ftlb)
Replacing the gear oil