Chimney flue repair before installing liner for wood burning insert
In my area a liner is required for a wood or pellet stove even if the flu is serviceable. I would have the cap made to protect what is left and the new liner will reduce any heat damage to those areas by being centered in the flu. Make sure to use solid or double wall if required, never use the flex pipe (looks like heavy dryer vent). that stuff really traps the creosote and there is no real way to clean it a standard brush just pokes them full of holes. I have heard stores in my area state that the flex line is legal but it is not here so even if the store offers flex at a couple of hundred dollars savings don’t use it unless you want a chimney fire.