Sick but still alive is their preference so they can humanely euthanize it and be in the best condition possible for testing. The one I sent to them had died overnight and I didn't find him until early the next morning, so he wasn't in the best shape even before I shipped him. If your third one is showing the same symptoms, it might not be a bad idea to take it there. That's easier said than done, I know. Sadly there's no way to diagnose Mareks on a live chicken.