We have a rescued Black Labrador (approx 8 years old). He's generally in good health, not overweight and relatively fit, but has a recurring problem with his ears. He gets a very strong smelling, black sludgy discharge, predominantly in one ear but affecting both. It causes irritation (scratching & shaking head). He has been treated for ear mites with drops supplied by the vet, but this was uneffective. We've also tried herbal drops, which helped to alleviate the soreness and reduce the smell, but they still failed to cure the problem. The vet has checked his ear canal and said it's normal. This has been an ongoing problem for several years, and we'd be very grateful for any suggestions