S510 xtra air leak

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I have an air leak coming from this location, right below the cap you unscrew to refill the cylinder. I am a noob at this, so looking for advice. It looks like it might be a bad o ring just below this location according to the air arms parts listings. Is this something I can take apart and replace myself. My dealer I believe is at the SHOT show so just trying to figure things out in the mean time. https://www.flickr.com/photos/147270397@N06/35542819336/. is the diagram and the parts list is. https://www.flickr.com/photos/147270397@N06/35542820606/ thanks for any input. Gameh