I unsuccessfully tried to post pics before. Will try again here.
Here's the PEX supply and return lines at the bottom of wall, under the nightstand and bathroom sink:
https://drive.google.com/file/d/1-z9...ew?usp=sharing
After I cut and spliced them to try and correct the reversed flow:
https://drive.google.com/file/d/1FY2...ew?usp=sharing
Discovering the massive leak above inside the wall, I began to open up the wall above. Here's the check valve hidden inside the bathroom/bedroom wall, access thru left overhead cabinets over bed:
https://drive.google.com/file/d/1mRJ...ew?usp=sharing
https://drive.google.com/file/d/1mSM...ew?usp=sharing
https://drive.google.com/file/d/1VH3...ew?usp=sharing
And here's the finished job with a new 1/2" brass check valve and fresh PEX tubing:
https://drive.google.com/file/d/1PSC...ew?usp=sharing
Works like a champ now.