I got to this post from doing a Google search for "Tero X 5.0 headlight mount replacement part". My bike has 500 miles on the odometer. While I didn't get an answer here, I got my answer at a Specialized bike shop. The replacement part is $6.70, so I ordered 2 of them. Then I went and looked at a Tero X 5.0 on the showroom floor to see what might have happened..... So if you turn the handle bars to full lock, There is no "lock." The "lock" is the headlight hitting the top bar of the frame at about 120 degrees of rotation. The mount is very sturdy with anterior-posterior loads, but with side loads it is very weak becuase of the leverage that is applied to the mount that has about a 1" drop and its dimensions are long in the anterior-porterior direction, but skinny in the lateral direction. This makes a side load devastating to the mount. So how did I get a big side load by hitting full lock on the sterring column? I put the bike in the back of my Tesla model S instead of putting in the bed of my truck. I was doing a trail that was 100 miles from home, so using the EV made more sense from a gas price stand point, my first time trying this. After removing the front wheel, the handle bars wouldn't clear the roof line in the hatch back unless I turned the handle bars 90 degrees. It doesn't take much more than 90 to hit the headlight on the top bar. So I am pretty sure that I cracked the plastic mount when putting the bike in or taking it out, when I was wrestling with it hanging up on the carpet. Then on my next night ride, I noticed the headlight was pointed off to the right by about 20 degrees. I thought it was due to a loose screw that allowed it to move. So I reached down and applied a little side torque to it to straighten it out and "pop". The mount was dead.
Eidt: I have Ergon GP5 grips, which make the handle bar clearance more of a headache when fitting it into the back of my car. Made the edit since I just noticed you have Ergon Grips as well.
No bell, lights, rear rack or a kickstand 
