In my experience as a welder through the last few years and with other pressurized systems, whenever you are trying to seat a regulator on a bottle as you thread it on, jiggle the regulator and this helps everything to seat properly. You don't need to be hercules and reef on it on there just hand tight and then a bit farther with a wrench. Also, every bottle has leaks, some big and small and even if you just leave it there to sit and dont use it for 6 months it will all leak out as all pressurized gases do. Another thing is that all tubing isn't perfect and slowly will seap out through microscopic holes. Although this doesn't constitute a major loss, but can contribute over time. Teflon tape isn't needed either as you stated although I would recomend getting a new washer as if it is crushed it is either a one time deal or just garbage and should be replaced. After that get the system up and running and spray it down with soapy water you will see where your leaks(if you have any) at that point.