If air is leaking around the threads of the on/off knob then it would be
caused by air bypassing either the o-ring on the tank pin or tank pin
retainer. These are highlighted in red in the below diagram. It is
likely that there is some dirt/debris on the o-ring which is
compromising the seal and a simple cleaning will correct the issue.
To remove the tank pin and retainer for cleaning, please refer to our MRS Maintenance video.