Well if it is the intake gasket, or whatever, it must not be a big hole. If it was I would get coolant in the oil and vice versa. None of that is going on.

 

It is more likely for a gasket to split or tear than have a large hole.
I'm out of ideas, as it seems with most of the forum here.

BTW, intake would create vaccuum and the pressure from the coolant would push it into the intake before air would be pushed in.
A head gasket would have to be bad for air to be pushed into the coolant, BUT, that would work backwards and burn coolant as well...
Like I said, I'm out of ideas.