The top view seems to show that the grain angle is in line with the pull of the strings, running with the width rather than the length of the rail, which is what seems to be causing the strange splitting - not a crack along the grain, but simply pulling the wood that is in line with the pin/string. I guess you could take that section and replace it. It seems to have been patched together every which way already, with the screws into the rim and the dowels going downward. I'm not familiar with Herz's instruments, so I don't know what is likely to have been original.
In any case, it is a structural catastrophe, and it needs to be made solid enough to resist the pull of the strings. I don't see any shortcuts, other than the notion of replacing only a section of the rail.
Regards,
Fred Sturm
"Since everything is in our heads, we had better not lose them." Coco Chanel