2000-2005 Yamaha F40B Outboard Service Manual, Page 114Get this manual
f.il1_L_O_W_E_R_U_N_IT _
LOWER UNIT
CHECKING THE GEAR OIL LEVEL
Check: Gear oil level Level is low -7 Add gear oil to the proper level
CHANGING AND CHECKING THE GEAR OIL
1Check: Gear oil Milky oil -7 Replace the oil sealSlag oil -7 Check the gears, bearings, and clutch dogChecking steps (1) Tilt up the outboard slightly(2) Place container under the gear oil drain screw (3) Remove the gear oil drain screw and gear oil level check screw