Here's a thought

The above mentioned squareness of the rocker machining needs to be ruled out. I suggest assembling the rocker that had a failed adjuster with one of the other adjusters and let it sit overnight again. If that adjuster fails also, you may have a machining issue, not an adjuster issue. I don't believe that is the case, but it has to be ruled out. Of course, simple measurements would reveal the same information, but nothing can argue with data from experimentation.

The galling and grooving worry me more than the adjuster issue. Good luck.