Performed preferred customer furnace cleaning. Found rust and water damage inside the furnace. Found that the black pvc fitting on top of the furnace was not glued. Applied pvc glue to the fitting. Cleaned the burners and the flame sensor. Wiped down the inside of the furnace. Checked the electrical. Cycled the furnace. Checked the gas pressure and performed furnace combustion test. The furnace is running normally at this time.