My name is Jon and I am an authorized AGA service tech and I can help you today.
Where exactly is it rusting?
inside or out?
is it possible for you to upload the pics here so I can take a look? just take some pics and use the paperclip icon at the top of the post here.
if the unit is chipped any where on the porcelain it then could start to rust prematurely. but either then that, this unit shouldn't be rusting at all.
Please get back to me here at any time and I will go over some more options