Have a vented gas fireplace. In dismantiling to replace the inoperative ignitor, two small cracks were discovered in the firebox. Have been told that we need to replace the entire gas fireplace icluding venting. Have been told that due to code cannot replace with an insert. Would it be possible to repair the cracks with JB Cold Weld. Have researched that cold weld will withstand 500 degrees F and 600 degrees for about 10 minutes. Any thoughts on repairing the cracks with JB Weld.