A technician is performing an oil change on a heavy-duty truck's differential. After draining the old oil, they observe a significant amount of black, sludgy material mixed with fine metallic particles on the magnetic drain plug. The truck has been operating normally, with no abnormal noises or vibrations reported. What is the most appropriate next step?

Question: A technician is performing an oil change on a heavy-duty truck's differential. After draining the old oil, they observe a significant amount of black, sludgy material mixed with fine metallic particles on the magnetic drain plug. The truck has been operating normally, with no abnormal noises or vibrations reported. What is the most appropriate next step?

Answer options:

• Flush the differential with a cleaning agent and refill with new oil. ✅ Disassemble the differential for inspection and component replacement.
• Top up the differential with fresh oil and monitor for further symptoms.
• Install a higher viscosity differential oil to compensate for wear.

Correct answer: Disassemble the differential for inspection and component replacement.

Explanation: The presence of black, sludgy material and fine metallic particles indicates internal wear, even if no symptoms are currently present. Disassembling the differential for inspection and repair is the most appropriate proactive measure to prevent catastrophic failure. Flushing might temporarily clean it but won't address the wear, topping up won't fix the underlying problem, and changing oil viscosity won't stop component wear.