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 :)