Brother HL-L8260CDN Online User's Manual page 326

9. Slide the belt unit back into the machine. Make sure the belt unit is level and fits firmly into place.
NOTE
To avoid print quality problems, DO NOT touch the shaded parts shown in the illustrations.
10. Make sure the green lock lever (1) is in the release position, as shown in the illustration.
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11. Gently slide the drum unit into the machine until it stops at the green lock lever.
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