I know the obvious thought is 8 needed (4 bottom/4 top) but my ETK CD shows 5 needed. That's 4 bottom and 1 for the pressure regulator. It doesn't indicate an "o" ring fits at the top. To further complicate things there is two different P/N for the "o" ring pictured (both show quty 5)The numbers are 220.127.116.116.708 (AE?) and 18.104.22.1680.767. Can anyone shed some light for me on this, please?? TIA..