I had a similar problem with my last dog, after steroids, antibiotics, creams etc for 3 years!! we were also told he was deaf in that ear from a suspected perforated ear drum and vet wanted to open up the ear canal permanently

on an afghan type coat!! He went in to have his teeth cleaned and I asked them to have a proper look down his ear as I suspected a deep polyp. Vet pooh poohed it but did the examination and
removed .....................a deep polyp on a very long stalk, they hadn't been able to see far enough down to see it as it was attached at the margin of the ear drum/canal. No more problems with ears :)
It would also be worth investigating the yeast avenue as Isabel has suggested.
Also one of my present dogs gets ear problems if fed on food which is too rich (eg puppy food to put back weight lost) as long as he's kept on less protein + fewer ingredients his ear is fine!! (but I would have thought Burns would fall into this category)