Hull may flex
It is correct that we want no flex of the hull-keel joint, or of the hull around the joint.But some flexing of the joint may occur. I remember discussion of this topic on another model. (check th archives). Certainly the joint is stressed if the boat is being moved on the hard, since it usually rests substantially on the keel. The glass can deflect, even a little bit under these loads, or in a grounding event, leading to the kind of crack you describe.Hunters from the early years have thick glass (around 5/8ths to 3/4ths of an inch for your model) and very solid grids of glassed in beams to hold the keel and maintain hull shape. So the discussions here have tended to agree with your pro - it's likely a cosmetic problem and not much of a worry!DavidLady Lillie