Leather ear is a type of fungus. I had a dog who came to me with black, leather like ears....his skin was also a mess! My vet had me bathe him in Selsun blue shampoo with a 50/50 warm water and vinegar rinse after. I was amazed at how it cleared up. You could simply dab that on his ears with cotton balls. Vinegar is acidic and fungus is a base..so that is why it works.
I had suggested this to Jencar98 in the past with one of her pups and it worked...so you might want to pm her and ask about it.