I've followed the Nutkin threads since Bonaparte brought him home and I was very sad when I saw this thread (infact, my heart sunk when I saw the tread title with Nutkin's name in the "last post" off the main forum menu. I know how hard it is when trying to figure out a mystery illness and was really hoping that in Nutkin's case there would be a simple solution found soon!
Nutkin thanks you for trying your hardest and is healthy now at the RB. He's a special little boy, so all the TCS RB cats will certainly recognize him when he gets there!
Edited to add: Maybe Bonaparte brought him home because he knew he needed some love before he gave up his battle. By the sounds of it, Nutkin fought well beyond how long he should have been able to in order to get as much care and love before he moved on.