Originally Posted By: Cujet
I'm 100% sure the clutch spring has nowhere near the number of actuations a valve spring has. Yet, we don't see valve spring failures often.
Valve springs are not subject to their coils being slammed together at regular intervals. Clutch springs are. That's the difference.
As I've said twice already, the telltale would be the appearance of the retaining lips on the friction disc's center carrier.
As for recycled steel, that has been used for many, many decades; it's old technology, and difficult to mess up, even for Red Chinese working under automaker specs. Anyway, ALL iron must be converted to a non-oxidized state, whether it's fresh from the mine or reclaimed from prior use. And flaws in steel can come in the form of streaks and slag inclusions, not necessarily corrosion; inspection of the fractured surfaces can reveal those.