As a side note to this, when I had my Radiator changed, I noticed that my overflow level didn't drop after cooling.
I realised that when Natrad changed the Rad, they had left the hose clamp off the nipple on the Rad where the overflow hose attaches.
Small clamp on there and everything syphons back and forth nicely.
Looking closely at the Japanese in the model codes, I get the impression it is a V spec. Not 100% sure.
I think the N in the model refers to this. KBNR32RBF NA
Before you spend dollars, check every related hose, pipe, connector etc for splits, cracks, loosness etc...
Tighten every hose clamp. If then you still can't find it, then seek the professionals.
I just pulled it all apart using the mother of all shifters. The ones holding the bar to the bracket were tight as Bro!
Especially tight were the middle bolt/lock nuts. Someone say, left hand thread?