My chimneysweep says I need to replace the lower section of my liner because of a gap in the inner part of the liner. This is a double-wall liner with an inch of insulation between the inner metal and the outer metal. All of the load is borne by the outer metal. Since the insulation is still in place and there is no reason for the gap to grow further, I am skeptical that I really need to replace it, even though he would need to recommend that to be on the safe side. What do you experts think? One photo is of my liner and the other is the Security Chimneys liner design. Thanks.