Thanks for the reply.
I just check it in the darkroom with a flashlight from different angles. I don't see the light from the auxiliary shutter. Also, the pre-lock of mirror will open the auxiliary shutter.
However, if I set the flashlight above the body and remove the waist-level viewfinder, then push the shutter button, I can see light in the upper part of body while the auxiliary is opening and the mirror is not fully up.
I discuss this with the repair center on the phone, but they think it's not the reason of the leak because the light is moving out of the body, besides, if the auxiliary shutter opens later, the expose of the film could be interfered.
I can not tell the opinion of the repair center is right or wrong.