Furnace clean and tune. Cycled system. Checked heat exchanger, found large areas of rust and cracks forming. Checked and cleaned burners, burners are very rusted and damaged. Cleaned flame sensor. Checked igniter, worn, but tested ok. Found leak in ventor motor/transition assembly. Ventor motor bearings are very worn. Normal levels of CO and XS air in exhaust. No CO found in airstream. Average life of this unit is 15 years. This system is 29 years old and very worn. Future failure is expected. Second opinion recommended. System is worn, but operating normal at this time. Job complete.