Re: Question about my current KM...
This won't affect your smoke, you are right, as there is a separate tube down the middle of the hookah.
BUT, this will rust out the inside of your hookah very quickly, chances are it already is. Now, the outside of KM's is very resistant to rust, but the inside I highly doubt is the same. I am not sure that this will affect anything over-all, because as you stated the shell is just being rusted on the inside, not touching smoke, water, hose ports, anything.
The only problem I could think of is that the water drips down onto the hose port tune (inside the heart) and somehow gets into tube and rusts the inside of it.
I think until your smoke starts tasting absolutely revolting, you are fine, and when it does, just don't use the ice chamber.
And I would try to find the tiny hole and seal it with epoxy or the likes.