Furnace clean and tune. Cycled system. Checked heat exchanger, found some rust and corrosion, but no visible cracks found. Checked, removed, and cleaned burners and flame sensor. Burners were very rusted. Cleaned as best as I could. Checked and adjusted gas pressures to maximize efficiency. Found Ventor motor bearings are worn and noisy. This may cause this motor to seize and fail. Normal levels found in combustion check. No CO found in airstream. Average life expectancy for this unit is 14 years. This system is worn and rusted. Found areas of evidence that there are leaks in this system causing rusting throughout the burner compartment. System operating normal at this time, but future failure is expected. Job complete.