Furnace clean and tune. Cycled system. Checked heat exchanger, found all chambers have large amount of rusting and deep etching. Several areas in chambers are showing signs of cracks starting to form. Checked, removed, and cleaned burners and flame sensor. Burners were extremely worn and rusted. Flame sensor is damaged and starting to melt. Igniter tested normal. Found large area of external rusting and water leaking from damaged Ventor motor. Bearings in this motor are very worn as well. Water is leaking into blower compartment. This is causing water damage very close to blower motor and main board. Checked and adjusted gas pressures to maximize efficiency. Preformed combustion test and found normal levels in exhaust. No CO found in airstream. Average life expectancy for this unit is 14 years. This system is well past that time period and is in very poor condition. Due to age, condition, and cost of repair, second opinion is recommended. This system is expected to fail. Job complete.