Does a single master link weaken a chain in any significant way? If it did, we'd have lots more chain failures than we see, and master links wouldn't have survived as a product. So, would adding one more master link (which is about 1% of the chain) increase the risk by any significant amount?

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"Go yell at an M&M"

I agree that a master link isn't any weaker than a regular link, but that's really not the point here. The real question is, why did that one plate crack? Without being able to answer that question definitively, I'd be concerned that more plates will crack and the chain could fail catastrophically. Seems like cheap insurance to me to replace the chain.

You said the bike is 'new', if so, I'd expect the shop to replace the chain since it appears that the chain was likely defective or installed incorrectly.

I get where the mechanic is coming from. If one link failed no telling if the rest of the chain is going to fail sometime down the road either it can be risky and if it fails at the wrong time you could end up in a nasty accident or fall. I'd probably think about replacing the chain too in this scenario..chains aren't that expensive unless you are getting some special friction reduced chain or the top level Wipperman Connex chains.

I have no issues using master links and one chain on my road bike has 2 master links (I screwed up sizing the chain and added some more back in with a 2nd master link....works perfectly find for the last 1000 miles I've been running it). I even keep spare master links in my emergency kit just in case.

It's a 1x11 setup, so the severity of the chain lines is somewhat inherent. I would imagine (again, I'm no bike mechanic) that if I start breaking multiple chains, we'd know there was a setup problem. I'd like to start anew (new chain).

The shop the bike was purchased at said they were going to replace a link. My preferred LBS mechanic (we were doing a trainer ride there, last night), said he would replace the chain.

Hence my inquiry. Thanks for the replies.

That's got to be pretty rare. If new, I'd take it up with SRAM. They should step up in these cases and fix the problem.

If the repair had to be paid by you, I'd replace with a master link and move on with things.

If it just broke as a consequence of regular operation, which would be pretty rare (i.e. not due to chain-suck, -cross, -jam), I'd def replace the chain, as it could be a dud.

Ask your LBS where you bought the bike, or call SRAM itself and you can probably get one replaced for free. What series is it? I generally run the 1031 which is SRAM's cheapest chain. When anything happens to it I just replace it NBD since it's cheap on Amazon or Nashbar.

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I still lapped everyone on the couch!

I asked both (LBS and SRAM). LBS (where I bought it) said he intended to replace a link. Other LBS (where I get most of my work done) said to replace the chain. SRAM says to replace the chain. Second time out on the bike, so it's under warranty.

I have no idea which chain is on the bike. It's a 2018 Specialized Fatboy (1X11 SRAM).