I'm having a hard time with this original post.
My wife and I just happen to own EIGHT Ferrets, so I'd like to think I know a little bit about Ferrets.
I do know two things about Ferrets, they are very smart, and they like to poop... but still, this post doesn't make any sense to me.
I also own and build multiple computers... knowing what a typical case is like, how it sits, and where components are and the size of a ferret.... I wonder...
1) Ferrets are natural corner-poopers. They always poop in corners.
2) Ferrets are also quite lazy when it comes to pooping... the nearest corner, or the "easiest" corner to get to is where they will poop.
3) Why would a ferret (as clever and lazy as they are), open a case to poop in when they are far more likely to just poop near the case (if it's on the floor).
4) Cables, wires, PCI cards, etc Even a "backing ferret" (all ferret owners knows what that means), how did an animal that big get it between the MB and the case? We're not talking Hamster droppings here... Ferrets leave land-mines.
5) Ferret Poo solidifies quickly and is actually very easy to get rid off, especially on hard surfaces like a computer case (even MB).
6) All Ferret Owners need to "Ferret-proof" their house... having Ferrets is like having a 2-year old in the house... they are that clever, that mischevous and that capable of getting into trouble. I have three desktops in the house... non of my eight ferrets are capable of getting into the cases (and I have some pretty smart ferrets)... lax security in the house? That case should have been "ferret-proofed".
7) I'm still puzzled how (or why) you got Ferret poop where you did between the MB and case and why it's so hard to remove. Ferret Poo is actually one of the easiest things to get rid of. It's a mystery.
8) Anyways, to answer your question... NAIL POLISH REMOVER... it's a computer-tech's friend... it'll get rid of almost anything and everything on or around computers, and it won't kill any of your components (it also dries quickly).
Good luck... and next time ferret-proof the house!