Yeah, don't bother replacing the gas lines unless you've clearly identified that as the source of the leak, which is pretty unlikely. as Zachattack says, it's almost certainly some point in your system where two separate objects are fitted together - somewhere in the regulator, the lid, a post, or the connection between the beer line and a hose barb.
A couple weeks ago I lost a good chunk of a CO2 tank when there was a leak at the nut of a flare fitting on a QD.
Get some water with some dish detergent diluted in it and spray every connection on your system. Guaranteed you'll find some bubbles and solve your problem.