Any chance you could post a better picture of the missing piece?
I would think if the E clip came off it would have been thrown out with the wood shavings rather than sucked directly into the clutch itself. The clip just seems to big to make it that far. Even if it broke in half I think its unlike to have been sucked in. Not saying it is not possible though. It would however make the entire clutch loose and run out of balance, to me it certainly looks plausible that this occurred.
I found this video that showed a piece of the exhaust rusting of and being sucked into the clutch area. Could you check the exhaust to see if that is intact? If it broke up into small enough pieces it could possibly make its way into the clutch.
https://www.youtube.com/watch?v=et8u-B0k8Zw