I agree with bobby_g. At one point this capacitor almost certainly took a light blow from the side. Could have been during assembly. (I.e., bumped by the butt end of an assembly tool) It obviously only caused hairline cracks initially. Then, as bobby_g said, inertia from some kind of a normal bump, rack jarr, blow, or whatever (likely in it's rack mount the unit was held firmly and when subjected to the blow or bumps, it was the weak link and simply let loose.) - (you know, like when you went 4x4ing with the rack laying in the bed of your truck.... LOL) I agree fully that this type of break would most likely have been initially caused by a light blow from the side of the capacitor. IMHO (was a Vishey Tech years back - we have seen it all)