yeah i mentioned this in another thread. The reason they have short spans and got diseases (my guess is that yours got Adrenal first right?) is because you fed the expensive ferret kibble. it has too many carbs in it. Ideally a ferret should be fed whole prey as they are obligate carnivores and plant matter is only doing them harm. most people i know that feed whole prey, mostly feed chickens and whole rabbits. there are various sites online where you can buy the whole prey frozen.
the one problem is that ferrets are picky eaters, if they've grown up eating kibble, its really really tough to get them to switch to a whole prey diet, they don't see it as food any longer. you have to basically starve them and force them to eat it.