It would appear that a company in Japan has solved the issue of not being able to replace the centre seal in a MC21 crank by engineering a Labyrinth seal to take its place!
Here is a link to the article which is written in Japanese but I have used Google translate which isn’t great but you get the idea....
https://young-machine.com/2018/10/21/15117/

Rugs also do bearings
http://tyga-performance.com/product_info.php?products_id=3647
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Why do things simply when you can complicate them

Interesting. Wish I could get my hands on one. Next is to make them ceramic.