The purpose of the hole is to indicate a bad waterpump seal,which I think unfortunatly is what you have.You will have to remove the right hand case in order to replace the seal,you should check the impeller shaft and see if it is badly worn,there maybe a grove cut into the shaft,you might want to replace the bearings(available from a local bearing shop #608 if I remember right)they are fairly cheap.You can try a quick trick that might help get some brake cleaner and spray a bit into the hole, it might swell up the seal and stop the leak.