Yeah, this so true depending on which one is buggered. The airflow direction servo is a different one to the temperature one (albeit a flap is probably involved somewhere as well). On my GS430, the air flow direction servo went (changed it last week) and that did make a clicking noise sometimes, but not every time.
If you are needing to change one, be sure to search fleabay by part number once you've found the right one. Second hand servos were expensive for the GS430, but they are the same part number as the IS200 one, which were much cheaper ;) I'm sure later models would share these types of components as well.
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