Arrived to furnace maintenance. Upon arrival I spoke with the customer who showed me the location of the furnace and corresponding thermostat. At the furnace I began by checking the systems static pressure. After this I checked the blower for proper operation and cleanliness. The blower wheel has developed substantial debris build up and the blower motor has developed worn bearings. At the furnace I found the thermocouple not wanting to stay lit. I performed a safety inspection of the burners and heat exchanger. The heat exchanger has started to deteriorate and I went over my safety with the customer and showed him pictures of this. I performed a combustion analysis finding a higher than normal CO as well. With the age and issues with this system I am having my supervisor out to quote replacement.