Bread maker paddle cylinder bored round; inner flat side gone

I have a Zojirushi BB-PAC20 two-paddle bread maker. It had been working fine for years, but recently it stopped mixing right, leaving huge chunks of unmixed flour. I found that the problem was one of the paddles; it rotated freely all the way around the post it mounts on, so when bread ingredients were there holding it in place, the post would have rotated freely within the cylinder, without rotating the paddle.
Originally the cylinder had a flat side, matching the flat side of the post it mounts on and which rotates the paddle. The paddle's cylinder had been bored completely smooth and round; no vestige of the flat side.
The other paddle had only a tiny nub remaining from the flat side; it would have failed in the same way soon.
My question is, what happened to the metal that had constituted the inner flat side of the cylinder? I'm pretty sure we didn't eat bits of metal, and I never saw bits of metal when cleaning out the pan and paddles between loaves. Where did that metal go?
UPDATE:
Tetsujin asked for pictures. Here's the paddle:
This shows the posts at the bottom of the pan that the paddles mount on:
This shows the paddles mounted on the posts:
Best Answer
After comparing the old paddles to new replacement paddles, all of them original OEM pieces from Zojirushi made specifically for the BB-PAC20, I believe the flat parts of the paddle cylinders deformed, spread around the inside until it was smooth and nearly round.
When I placed the new paddles on the posts, I found that they were a little looser than the old ones. Again these paddles should be exactly the same. It wasn't a big difference but it was unmistakable as I tried both old and new back and forth. Looking again inside the cylinders of the old ones, I think I see evidence that the flat part was spread around inside until it was smooth and nearly round.
I've had the old paddles around three years, averaging a loaf a day. The change in fit tightness must have been very gradual as I didn't notice it.
I think it makes sense that the paddles would be made from a softer metal than the posts, so that the paddles sacrifice themselves to avoid damaging the posts. I see no wear to the posts. It would take a lot more work to replace the posts than replacing the paddles.
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When should I take the paddle off my bread machine?
The best when to remove paddle from bread machine is before the final rise. It is definitely possible to remove the kneading blade from the bread maker before the bake cycle, you just need to time it well. This can be tricky to get right, but once you do, you're set for life!Why does the paddle in my breadmaker get stuck in the bread?
If you have a newer design but it sticks in the bread and is hard to remove, chances are the anti-stick coating is worn and you will have better luck with a new replacement paddle. To find a new replacement paddle, just google the bread maker's make and model name, and the word paddle.Why is my bread machine not working?
Too little yeast, your bread won't rise sufficiently; too much, and it will rise and collapse. It's important to watch your dough as it rises and bakes; dough that has risen and collapsed may look just like dough that never rose at all, once it's baked. In order to correct the problem, you need to know what went wrong.why we should remove paddle from bread machine just before baking start
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Answer 2
From my comment
It depends which way up the 'plug' & 'cup/socket' are. If the 'cup' faces down, you ate it. if it faces up, you probably washed it down the sink when you cleaned it. Pictures would help.
After pictures added…
You ate it.
It's very unlikely to do you any harm.
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Images: StockPhotosHub.com, Anna Shvets, Andrea Piacquadio, Andrea Piacquadio