Furnace clean and tune. Cycled system. Checked heat exchanger, found all three shots are very rusted with cracks forming. Burners are damaged causing some flames to fire on the wrong side of the ribbon guard. Sparkler is weak, but tested ok at this time. Found water leaking from ventor motor and draining onto the electrical supply box for furnace. Cracked ventor and bearing wear. Drain was plugged. Standing water in blower compartment. Tested for CO in airstream, none found. Normal levels of CO and XS air in airstream. System will fail. Average life of this system is 14 years, this system is 26 years old and in very poor condition. Due to age, condition, and cost to repair, second opinion is recommended. Job complete.