I work as a vet tech at a vet hospital while I am finishing up my pre-reqs for vet school. I see this stuff quite a bit and I can tell you what I would do with it. Well, it could be a few things. Ear mites are a possibility, but are usually followed with a constant head shaking and scratching at the ear...which can lead to broken blood vessels and a collection of blood int he ears (especially in floppy eared mutts). If you have access to a microscope, take a sample of the ear debris (if its mites it will usually be black in color), apply to a slide and check it out under 10x or so. Mites will be easily seen. If it is mites, a quick prescrip. ear ointment will clear it up. There are several over the counter ear cleaning solutions..and they work well. Apply a good amount to the ear/canal...massage the solution in and gently remove debris with cotton. Another option, to get a really good cleaning, is to apply a mix of warm water/dish soap/betadine to the ears. This is usually accomplished with a turkey baster or water pik. Seeing as though you have a crazy lab, chances are this will be close to impossible to accomplish effectively without sedating the animal. Your best bet would be with the ear cleaning solution picked up at the vets office, and applied by you FREQUENTLY and EFFECTIVELY. Stay on top of it and you will avoid infections etc...
P.S. I have yet to attend vet school so this is not professional advice, just what I would do..
my $.02
hope it helps