It is true about the ear mites and mineral oil.
But in my experience a lot of these cases are not mites.
A quick vet visit will rule out the ear mites.
Much of this is due to allergies or a drainage problem. Just like frequent ear infections in some children.
If it is not ear mites, I have found Zymox to be the answer to chronic infections or problems that stem from allergies or the drainage problems.
I have used Zymox as well. Love it. I usually use a mineral oil for a while (unless it is really bad which I never let it get that far :)) If that doesn’t clear it up, I have athletes foot cream I use and that will clear up a yeast infection.