I have an Essex Thermo wood furnace that has been working well for 7 yrs. Recently, the inlet air damper did not close all the way and the fire continued to burn opening the relief. I cleaned the damper area of creosote but found that the damper blade slid down as it closed and hit the lower frame preventing it from closing. The drive motor works, but it appears that there should be a hinge at the top of the blade to keep it closing properly. there isn't anything that looks like that. I don't have any literature to show how it should be. Any suggestions?