There appears to be a channel leading to that hole. Can’t say that I remember its purpose. #16 is a seal to keep water & exhaust from blowing out but that doesn’t seem to be where your bubbles are coming from.
EDIT: the channel seems to be the cooling water exit(??) But I still don’t understand the bubbles hole. Or is there really a hole? Perhaps I’m seeing a hole that isn’t there. If no hole, probably simply a leaking gasket
