I have seen that info posted either here or on TrainOrders. Maybe do a search. I remember hearing about the different class repairs from my dad years ago. Seems like I remember new flues every 3 to 5 years, so its probably in one of the class repairs, maybe class 3.
Good to see you posting again Michael. Your post about 42 inch gauge in South Africa reminded me that when down there shooting steam pics you quickly forget it's not standard gauge. Although I suppose they consider it so.
Greg