It sounds like this is an example of an early 2012 chassis with the bolt-in brace together with the more recent extra gussets - the crack described seems to be the one the bolt-in brace was designed to prevent and begs a question on whether the brace is an adequate solution for an early car where a crack/cracks may have initiated but not propagated. From this one asks how many cars with the original (hopefully braced) chassis are still out there...
We were "lucky" in that our v early one cracked and had the chassis replaced
