Furnace clean and tune. #1. 3079. Cycled system. Checked heat exchanger. Found all chambers extremely worn and rusted. Deep etches found and cracks starting to form. Checked, removed, and cleaned burners and flame sensor. Checked and cleaned sparker. Checked and tightened electrical connections and clamps. Cleared drain lines. Found ventor motor bearings are worn. Leaks from transition assembly, possible cracks in assembly. Found evidence of water damage in blower and burner compartment. Checked and adjusted gas pressures to maximize efficiency. Preformed combustion test. Found CO levels very high. Levels were between 115 and 125. Also found XS air levels near 200. This is a very strong indication of secondary heat exchanger blockage and/or primary failure. Average life expectancy for this unit is 14 years. This system is over that expected time line and is in very poor condition. Furnace clean #2. 2003. Cycled system. Checked heat exchanger. Found all chambers are worn, rusted and ha