The stock centre plate of the RB25/6 gearbox can flex in high torque, high grip situations such as aggressive launches or high speed cornering. When it flexes the shafts (mainshaft and countershaft) come out of alignment and the gears destroy each other. The billet centre plate improves case rigidity. It's basically a full rebuild to install, so would be done with a bearing and seal refresh as a minimum, check synchros etc.