One of my first Japanese knives was from Moritaka.
I have a Petty, Gyuto and Nakiri.
I have heard of the problem Dave mentioned but i never had it on my Moritakes. I have seen the problem on some of my customers knives.
Like Dave mentions they are just not fixable !! If you have that hole in your knife you have to grind behind it to remove that hole completely.
So i thought i was pretty lucky because all of mine 3 Moritakas did not had that issues.
I used my Moritakas a lot, so i probably used 2 or 3 mm of my knifes, and guess what the hole problem showed up after that
So just to remind you all, that hole problem is real on Moritakas and it can even show up after you have used your knife for some time !!