Upon arrival unit was on and running. Customer stated they had an oil delivery recently. Checked oil flow and had ok flow. Checked the oil filter and strainer and found the filter was good but the strainer was covered in sludge. Replaced the oil strainer. Checked the nozzle and found carbon buildup on the tip and some oil in the blast tube indicating the nozzle went bad, most likely from some sludge getting in it. Replaced the nozzle and bled the oil line. Started and tested the unit. Unit is working properly