repaired my NOS(mfg date oct1994) actuator after renewing it last summer. picks the dead of winter to crap out. the spline(?) adaptor between the actuator and door arm shaft splits and breaks off. found the pieces inside the blend door duct after removing everything this time. I really wanted to understand why the new part failed. wrapped it with 0.025" safety wire and then slathered the wire wrap with epoxy. works like a champ. as to why the brand new actuator part broke i am looking at the massive amount of foam rubber on the upper and lower blend flaps. the motor unit drives the flap hard into the heater core to seal off the heat during a/c ops and maintains torque on the door operating shafts when they doors are held against the heater core. there is zero physical stops on the motor, so if it loses position, the computer drives it to the software derived limit and snap! one, poor design on the adaptor to the shaft with stress risers designed into the "keyed" coupling. two, no physical stop in the geartrain or limit switches in the module. three, the necessary smothering of the heater core during cold air demand. four, plastics age over time and they get brittle, just a fact of life. five, did ford learn their lesson and design a better unit? the short answer is no they did not.