Furnace clean and tune. Cycled system. Checked heat exchanger. Found all chambers are worn and are rusted. Deep etching found in all chambers. Checked, removed, and cleaned burners and flame sensor. Checked igniter. Found it getting weak and worn. Checked and adjusted gas pressures to maximize efficiency. Checked and tightened electrical connections and clamps. Cleared drain lines. Found ventor motor bearings are worn and noisy. Found water damage from leaks in transition assembly. Preformed combustion test and found higher levels of XS air in exhaust. This is an indication of blockage in secondary heat exchanger. No CO found in airstream. Average life expectancy for this unit is 14 years. This unit is past that time frame and is worn. Future failure is expected. Due to age, condition, and cost of repair, second opinion is recommended. Job complete.