CF Tank Repair

If it is leaking between the valve and the tank the o-ring that resides there is the most likely cause. Drain the tank completely remove the valve and replace the o-ring. Use no sealant when replacing the valve pressure and the o-ring will seal it fine.

If it is leaking somewhere in the valve itself once again it is likely and o-ring once you figure out how to get to it and replace it things will be fine. Lots of information on the net for this kind of DIY repairs.
 
Does it leak while the tanks valve is closed?

No sir. Only leaks when you crack open the valve to start filling.

Probably as easy as unscrewing the gauge and putting a new one on, if not just making sure the current was is sufficiently snug/tight.

If you not comfortable doing that yourself, any dive shop could do it in a couple minutes. 
 
If it is leaking between the valve and the tank the o-ring that resides there is the most likely cause. Drain the tank completely remove the valve and replace the o-ring. Use no sealant when replacing the valve pressure and the o-ring will seal it fine.

If it is leaking somewhere in the valve itself once again it is likely and o-ring once you figure out how to get to it and replace it things will be fine. Lots of information on the net for this kind of DIY repairs.

Thank you!
 
On mine tank (Joe broncato, air tanks for sale, tank) there is a small vent hole under the fitting that is screwed into the valve that leads to the fill hose. If that fitting isn’t tight it will allow air to leak out the vent hole Only while filling. Try tightening the fitting a little more. Have that happen a couple times. I tightened the fitting a little more and the problem went away.