You've probably already gotten a lot of responses, but here's my 2 cents.
My Rocky is a very fussy eater too and when I tried to keep a rescue, he
stopped eating.  I gave away the other ferret and got him new food, which
he ate.
 
I have noticed that Rocky prefers more meat based foods; he loves Bob
Church's Chicken Gravy (you should make it), a certain brand and flavor
of canned cat food, raw egg yolks and probably baby food (can't remember
if I gave it to him when he stopped eating, but I think so.) He also
seems to prefer foods in liquid form.  He is thin also, so when he
refuses to eat kibble I put some Ferretvite on it.So far I have tried 5
kinds of food and Rocky is only 2 yrs.  old.
 
I don't know if this will be of any help because your fuzzy may have a
medical problem.  You will know that if his behavior has changed and he
doesn't act normal.  Could he have a blockage?  Something may be wrong
with his digestive system if his poops are always seedy.  Rocky has them
occasionally, especially if he's had some fruit before eating, which
probably disturbs his digestion.  Are you giving him any treats like
that?
 
I hope this helps and that he gets better soon.
 
Shron & Rocky
[Posted in FML issue 4157]