Many warranties are only valid if purchased from an authorized retailer. In those cases where a part is sold by an unauthorized seller, the warranty isn't voided, it was never there.
You can bet that Shimano's lawyers have been consulted about whether or not they can legally differentiate between authorized and unauthorized supply chains related to warranty coverage...
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Slow Ride Cyclists of NEPA
People do not seem to realize that their opinion of the world is also a confession of character.
- Ralph Waldo Emerson