I heard from Aluminess. They said they would fix it. I live in Utah so getting it there might be a challenge. Might need to find an excuse to drive to CA.
It is very odd and I was pretty puzzled when I first saw it. I assumed someone had backed into me. However, as I mentioned, not a scratch anywhere else. Also the failure mode is consistent with a 'pressure' related pipe failure. Anyone who has had frozen pipes has seen that same behavior.
How water got in there is the real question. This is not my first winter with these parts. In hindsight, this summer I do remember hearing an odd hissing from the bumper when it was hot. This implies there was pressure being released. There are only four holes in the tubes all of which are where the box mounts. Clearly, the water level was higher than the bottom of the box based on the vertical crack. It also means there was quite a bit of water in there!
No idea how it happened. The Aluminess guy mentioned they would drill some drain holes. Odd but, probably a good idea!
If anyone is driving through Utah headed to CA, let me know!