When reading Philips post, I noticed that Wiscos asked a chassis question which went unanswered, if you haven't found out yet, the chassis that were mainly cracking, and from what I can gather, is that the main difference between '12 and '13 cars is that the front end has some gusset triangles welded in, whereas the earlier cars did not. They all had the bolted in bracing bar, so this is not necessarily an ID item.
As a matter of interest, the fact that MMC welded in gussets shows that they were aware of chassis weakness at a very early stage of production, in fact one of the dealers told them about a breakage on one of the first dealer demo cars to go out, and got very short shrift apparently.
