Pretty much answered yourself...Granted it doesn't get exercised too much.
Once (if) you get it working, re-position it.
Try a multi-vibe tool in contact with it while torquing the knob both directions. Maybe that will free it up.
Ok I understand now.Pretty much answered yourself...
Also drain tank as recommended in manual or might be a sticker on tank.
But what the comment on spring at 12 o'clock, turn regulator knob to the sky. Relocate the gauge. Likely another plugged hole to still have it visible
