Air leak.....what to do next?

[SBTork]

I am having some issues fixing an air leak in my system. My system currently consists of an air tank, 4 bags, and manual paddle valves for each bag along with two dual needle gauges. For now the compressor is not wired up but should be later today.
I have a fill valve on the tank and one line going from that to the paddle valve switch panel where it t's to two t's, one for each bag. My LF bag seems to want to leak down to nearly nothing after about 2 days. Last time I tracked it, it leaked down 2 lbs in 2 hours. So far, I've switched out the air bag itself with a new one and also replaced the paddle valve. I think the only other thing I can replace is the air line itself, but as with everything else i've done, I am not sure that's it. The fitting on the bag has good quality thread sealer on it, it's tight, all the lines are tight in their fittings.....

I am not sure what else I can do other than replace the line and see what happens. Anyone have any ideas?