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It could also be polyps in the middle ear or carcinoma (let's hope just the inner ear polyps). You won't be able to see these on your own, but your vet will with a quick and simple office visit.
If you've caught this early enough, and it sounds like you have noticed it pretty early, an antibiotic may be prescribed. It's very important to follow through with the vet visit though because these polyps can block the ear canal and impair your cat's hearing. They can also worsen, causing such severe problems that you have no option but to have surgery. The antibiotics are far less costly.
The fluid you're seeing could be the result of a burst polyp (if you smell your cat's ear it probably really stinks).
One thing to warn you about though - once you start the medication prescribed (depending on what your vet finds), give it meticulously throughout the whole course. Even if you notice improvement - don't stop. Otherwise the infection will just come back even worse than before and end up harder to treat the second or even third time around.