Leaking co2 tank

Got my 5# co2 tank filled at a local welding place yesterday. The associate brought it out from filling it and it was leaking already. So I obviously said something he brought it back out with no leak. Today I open the keezer and I hear a co2 leak. It sounds like its coming from the collar, where the brass meets the cylinder. Should I bring the tank back to the retailer? Or is there a way for me to tighter the neck myself. I'm a little hesitant to mess with the tank because of the amount of pressure the tank is under. Any help would be appreciated.

I agree, too dangerous to mess with it, and the odds are if the sales droid couldn't get it tight you won't, either.

Take it back.

Cheers!