I've never heard of "melting" the hoof before, but I suppose it was worth a shot. I think putting a "v" in the wall only adds to the pressure on the weak area. To demonstrate, hold your first two fingers together, hold them vertical to the table and push down. Now do the same thing, but with your fingers about 3/4 - 1 inch apart at the bottom. What happens? Personally, I think it works better to rasp the hoof wall (down vertically from the top) very short where the crack is and 1/2 inch on either side; blend in to the rest. Now the pressure is not pinpointed on that one spot. Maybe that will give the hoof a chance to regrow properly.