That's a very well written article, the writer did a good job detailing the problem and explaining how Boeing and the FAA are dealing with it post-inspection.
I've worked similar issues in the past. They are working diligently, looking at the failed part to determine the nature and cause of the crack. The article didn't say if Boeing makes the part or buys it from a supplier, but either way they are currently conducting a quality audit looking at everything from metallurgical properties to manufacturing processes of the part. Hopefully they find the problem is limited to a production lot, that makes it easy to do a swap out of the part.