I recently bought a hangar with a bi-fold door. Raising it is fine, as is lowering it, but when the door is coming down, if I press the "stop" button the door continues to lower for 5-10 seconds before finally coasting to a stop. This seems odd and wrong, and potentially dangerous. The motor and gearbox is located in the ceiling at the middle of the door; I have a powered lift and can easily have a look at it but not sure what I'd be looking for. I thought there might be some kind of adjustment but didn't see anything obvious. Anything in particular to look for? This is an "aerolift" door and was installed in the mid 1990s.