NEC Super Script 4400 Maintenance Manual page 244

22. Black Stain - Back side of the print paper is stained.
Main Causes
1. Cleaning pad is stained.
2. Fuser oil is low.
3. Fuser roller and back-up roller is stained.
Countermeasures
1. Replace the cleaning roller with a new roller. (See Chapter 6)
2. Clean the fuser roller and back-up roller.
3. Replace the fuser unit with a new unit. (See Chapter 6)
Fusing Unit
Cleaning Roller
Back-up Roller
Oil Bottle
Fuser Roller
Imaging Artifacts 235