Thank you for giving us more information.
Since he is 10yrs old - most likely his symptoms are more age related than from disease.
I would add poultry vitamins to his diet once a week, but if he has thrived this long with what you have been doing, I would not change anything.
It sounds like...
What do you feed him?
How have you treated him for Wry Neck?
You mention that he is able to walk again - was he not able to walk for a period of time?
Check his crop to make sure it's emptying overnight. Offer a balanced poultry feed along with poultry vitamins that contain vitamins E and B1...