There are two bolts (both 10mm I think), the one you found on the top and another on the bottom. Once you pull it off spray the inside with some Berryman's B12 and maybe even a light scrubbing with an old toothbrush. Basically you just want to remove any buildup around the valve. I also gave it a shot of silicone lubricant. Tighten it back down and you should be set.
