Bartender Geek

Besides, IIRC, you asked your vet about it, and he confirmed that there weren't any mites present. It's fairly common for cats with a history of ear mites to continue secreting the dark waxy gunk after the infection's cleared up. Allergies also can cause this.

This is not to downplay plumtreeblossom's point. if there's anyone reading this who has a cat with dark waxy buildup in their ears, who hasn't already had it checked out by a vet, please get it looked at. Ear mites can cause permanent damage if not treated. The ear mite stuff you can get at a regular store is fairly harsh, as is the grocery-store version of ear cleaner. You're better off getting something from your vet, or getting your vet's advice on what to buy at a pet store.

Hugs to you guys, and skritches to Boopsie, please!