Furnace clean and tune. Cycled system. Checked heat exchanger, found heavy rust in all three shots. No visible cracks found, but heavy etching and deep rust spots where cracks will form were found. Found flame sensor worn. Ventor motor bearings are worn and motor is running very noisy. No leaks found in system. Checked for CO in airstream, none found. Normal levels of CO and XS air found in exhaust. Average life of this unit is 14 years, this system is 15+ years old and worn. Future failure is expected. Due to age, condition, and cost to repair, second opinion recommended. Blower motor worn and loud as well. Job complete.