I'm so sorry that you have had to go through this. I understand exactly what you are going through. I had a wild caught White Front Amazon, I too thought she would be with me forever. She was my best buddy for 25 years. It is stressful when they are ill and feeling helpless. Her illness is what brought me here to AA as well. Paco is a stinker, he probably would like another bird around, shoot he is such a scaredy cat he would probably sit there and shake. Has the vet done blood work? It concerns me that you say the vet put him on medicine for arthritis and vinegar after months of low energy. Why did the vet wait? I wish I could get Paco to play and chew. He is terrified of everything. I did discover he loves to chew on books! So I clip a paper back book to his cage and he goes to town! I would keep giving him warm foods, sweet potato is full of vitamin A. So I'm a little confused, Walter is ok except that he isn't eating much? I would follow up maybe with a different vet if possible and offer Walter a variety of food. How is doing today?