I have made and sold about a dozen Vertex pens. I have had one come back, it was dropped by the user and broke the white mechanism off in the end cap.
Not my idea; but, there is a simple fix for this.
Take a round tooth pick and sand it down a bit to fit inside the white mechanism from the top. Measure the length, then cut a bit short. A little ca glue on the tooth pick part and put it in. This will reinforce the internal parts. I dropped my own Vertex, it hit on the click end, and did not break on the inside. It worked for me. After the first few I made, I have done this on all the others. Not had one come back recently. Still my favorite click because it is quiet and smooth.