I would guess you can just walk into Sears and warranty it- just exchange it for a new one.
At least in the states, this is the warranty statement: If this Craftsman hand tool ever fails to give complete satisfaction, return it to any Sears store or other Craftsman outlet in the United States for free repair or replacement. This warranty gives you specific legal rights and you may have other rights, which vary, from state to state.
Never had a problem on warranty issues with Craftsman (haven't needed to use it much, either), but a good number of people on this board have had issues... I guess certain store managers believe they can warranty what they want, and not follow the warranty statement...