Furnace clean and tune. Cycled system. Checked heat exchanger, found that all three shots were heavy rusted with cracks forming in all three. Checked and cleaned ribbon burners. Cleaned and checked sparker. Found that worn as well. Above normal rollout of flame on start up. Not enough to trip sensor, but flame does come past box edge. Ventor motor bearings are worn. Grinding on start up and some on shut down. Checked for CO and XS air levels in exhaust, both normal. Tested for CO in airstream, none found. Average life of this unit is 14 years, this system is well over 20 years and very worn. Failure is expected. Second opinion is recommended due to age, condition,and cost to repair. Job complete. Second opinion scheduled for today. No charge for service pending results of second opinion.