Problem: The mechanical C8.3 (2-valve head) is prone to cracking between the valve seats, specifically on cylinder #3 and #5. Fix: When buying a used engine, do a cooling system pressure test. Aftermarket heads (AMC) are actually stronger than the OEM Cummins heads for this chassis.
Problem: On rotary mechanical pumps, the governor ring turns to glue over time. On CAPS electronic pumps, the fuel actuator fails. Fix: Run clean fuel. Always. Fit a secondary fuel/water separator before the factory filter. For CAPS, keep the lift pump (fuel transfer pump) pressure above 20 PSI or you will fry the injection pump. cummins serie c