Increased sleeping is an indication that a bird could be ill, but it’s possible that Indy is just getting older and needs more sleep. That is not uncommon behavior for older birds, but I’m glad he is going to be seen by another vet just to make sure he is all right. Better safe than sorry.
Birds are really good hiding illnesses. There are two good ways to help determine if a bird is sick. The first is checking their droppings for any changes. Have you noticed any changes in their shape, color and consistency? Since you have your bird in an aviary with other birds, you may want to separate Indy at this time, so you can monitor his droppings. There is a sticky on this which may help you identify what to look for.
Also, do you know how much your bird weighs? If you have a gram scale, you can weigh your bird to see if there are any noticeable fluctuations in his weight. A good time to weigh your bird is first thing in the morning, after his first droppings, and before the first feed. If he is losing or gaining any weight, that could be an indication of illness.
Indy is beautiful. It’s sad to think he suffered like that. It’s a heartbreaking story, but thank goodness Indy was lucky enough that you found him. He has a good life with you after years of loneliness. You really need to be commended for that.