I did the repair today and was 3-for-3 leak-free connections.
This is what I replaced:

and this is what the valve looked like after I cut it out:

This is the tool (from Home Depot) that I used:

Here's the back view of the new part:

Look on the right to see the crack where it leaked. I think the original installer put one turn too many on the fitting and it eventually cracked. I tried it on the other side and got about 95% of the way around and the fitting cracked on that side:

If you're going to use a brand new blade in your utility knife to cut the pex, wear heavier gloves than I did:

I could have gotten the tool back into the plastic pretty easily for a return, but I'm going to keep it - just asking for more leaks if I return the tool :)