Don, all of what Al said, X2.

One of the big culprits for leaks is the quick connect fittings. EVERY time I remove an air line from one of those I cut off about 1/2" before I re-install the line. That gives you a clean, undamaged surface for sealing.

My little CO2 bottle sits for weeks at a time without being turned off. I haven't turned it off since I left Vegas and the high side guage still reads 900 lbs.

I fill it from a 30 lb. bottle with a whip (hose) I bought years ago for about $50. I haven't re-filled the big bottle for 12 years.