30 years ago, when my first Cocker puppy came to me from his breeder, she recommended Benzyl Benzoate Lotion as the best ear cleaner for Cockers. It's so long ago that I can't remember how I applied it or if it needed to be diluted or whatever. But either it was effective or my Cocker didn't have any ear problems, because his ears were always clean.
However, I haven't used it for probably 25 years or so! I've never heard of it for use in getting rid of fleas. I wonder if it's one of those old fashioned remedies that's no longer recommended for some reason?