You might want to confirm that it isn't the amplifier or crossover before concentrating on the compression driver. Use a known-good amp and crossover so you can be sure that isn't the cause. Once you've isolated the trouble to the driver, you can repair it. But it would be nice if you found out your problem was just a $5.00 capacitor.So I'd make sure it wasn't something else first, and then once I was sure the problem was the midrange horn, I'd remove the midrange horn, open it up and and inspect the diaphragm. If the surround is cracked, you'll be able to see it.
If you're uncomfortable taking the compression driver apart, perhaps take it to a repair shop for inspection.