The variator works by hydraulic pressure from oil contanied in it. The oil seal wears allowing the oil to drain, and all of the parts of the variator slop about. Hence the Ratle until it fills up with oil again. Also if the seal is worn it may not hold enough pressure to move the cam timing even when running as the oil can seep past the seals.
I think the Gear with the internal teeth moves along inside the inner shaft, and because of the spiral on the outer, it forces it to turn, taking the cam with it.
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