I replaced my back refractory panel and there is a small gap between the bottom panel and the back panel and a small gap between the left panel and the back panel. Probably 1/8 to 3/16 of an inch. Is this normal or does it need to be sealed?
This gap is indeed normal and is designed to be there for expansion purposes. Early designs where tighter in fit, but manufacturers soon discovered that the panels would bow out and crack from thermal expansion.