Brother T-8421D Instruction Manual page 21

NOTE
If the lubricating oil level drops below the bottom (6) of the oil gauge window (5), be sure to add more oil.
Adding oil to the oil tank
9
Remove the rubber cap (1).
10
Use the accessory oil tank (2) to pour in lubricating
oil until the oil level reaches the top reference line
(4) of the oil gauge window (3).
11
Replace the rubber cap (1).
NOTE
Be sure to add more oil if the oil level is below the lower
reference line (5).
Lubrication
12
Apply 1 - 2 drops of oil to the places indicated by the arrows.
<Minimum lubrication type only>
NOTE
Do not apply oil for semi dry types.
8