I would tend to agree about replacing the cassette after 5k with the chain. But it depends on how the cogs look. Likely the old cassette caused this problem, but I'd still recommend a new SRAM Chain and a new cassette.
The love Shimanos components...except for their chains. All my SRAM chains are hollow pin models and I've never broken one or the power links that come with them. Once you start using the SRAM chains and power links, you'll be hooked!
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