You're a good man, Rich, and Bruno is lucky to have a friend like you. If you suspect he might be craving something, there may be a way to find out what that is. Failing a blood test revealing a deficiency, perhaps offering a range of treats with each based on something a little different than the others might reveal more information.
Dogs lick their wounds, and pain he can't reach with a lick, or that is too painful to reach, might be soothed in his mind by just the act of licking. Are there any tender spots in hard to reach places? If he has chronic pain in his joints - not uncommon as we get older - CBD oil and other analgesics may restore some spring in his step. More than this I cannot realistically speculate about.
I think you are just as lucky to have him as he is to have you.
Thanks!