Furnace clean and tune. Cycled system. Checked heat exchanger. Found heavy rusting and etching in all chambers. No cracks found with camera, but found damage throughout all chambers. Checked, removed, and cleaned burners, flame sensor, and sparker. All three were ok, but all three are showing signs of getting worn. Checked electrical connections and clamps. Tightened all. Found very heavy rusting in both burner and blower compartments. Ventor motor has signs of leaking from the side and back of the motor compartment. Water damage and rust is throughout the entire system. Damage found on transformer and near the recently replaced main board. Found Ventor motor bearings to be worn and damaged. This may lead to the motor seizing. Checked and adjusted gas pressures to maximize efficiency. Preformed combustion test. Found that the amount of XS air (unburned combustion air) is higher than desired. This leads me to believe that there is some blockages in secondary heat exchanger, or a small c