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As been mentioned, it is not the chain but the guides which fail. They turn brittle, break which in turn causes the chain to possibly jump catastrophically.
There is an updated chain tensioner which is said to help. Theory is that it keeps the chain tighter against the guides as they wear. A looser chain slapping against a brittle plastic causes the fracturing. I have never seen an official BMW explanation, this just what I've put together over the years, but it does seem logical.
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2003 X5 4.6is Estoril Blue
2005 Infiniti G35X
1972 Datsun 240Z
1991 Isuzu Impulse XS Sold
1972 Fiat 850 Spyder Donated
1972 Datsun 240Z Sold
1972 Datsun 510 Sold
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