In TCM (Traditional Chinese Medicine) chronic ear infections in dogs stems from the liver or the immune system. Left ear = liver, right ear = compromised immune system. So how are Duke's and Chief's livers and immune systems, have you done recent blood and urine tests? Have you tried using CS (Colloidal Silver) drops in each ear; 2X daily for 7 days?
And yes, switch the kibble to a LID diet - a meat protein that neither have ever eaten, with no grains and wheat.
Good luck!