Furnace clean and tune. Cycled system. Checked heat exchanger. Found all chambers are rusted and corroded. No visible cracks found with camera. Checked, removed, and cleaned burners and flame sensor. Found burners are very corroded and rusted. Cleaned as best as I could. Igniter tested ok, but is showing signs of getting worn. Checked gas pressures. Pressures were a little low, but combustion test showed normal levels found in exhaust. No CO found in airstream. Found blower motor bearings are very worn and seizing. This will cause failure in the future. Ventor motor bearings are worn causing vibrations and noise. Average life expectancy for this unit is 14 years. This system is past that and is showing signs of major damage. Due to age, condition, and cost of repair, second opinion is recommended. System operating normal at this time. Future failure is expected. Job complete.