Drowningman
War Child
Try switching to wet food for a while and see if that works. My parents cat was throwing up every day and once they switched to wet food only she stopped. Some cats have a harder time digesting dry food.
I don't know if he's having any problems with his dry food though as he's been eating this stuff for about 10 years now.
Not sure how he would react to just wet food because he does snack on his dry stuff through the day and would probably think he was being punished or something if his dry food bowl suddenly went missing