Hi, I have a '74 FJ40 and recently acquired the missing heater duct from the fan to the heater core. I now have heat which is fantastic since we live in Seattle however when the fan is on high, the lower flap on the heater core will not stay closed and I do not get proper air flow to the windshield. Is there an adjustment which can be made? Thanks so much for all your comments and have a wonderful Thanksgiving! Eric