Can just be seals. If its leaking from the seals, order Fox air can seal kit off TF Tuned or Mojo, about £20. 15 minute job to do at home, and very easy.
ps when you say it loses air and drops back to 180, is this with the pump connected and you see it go down? If so, could be issue with pump. Noting also when measuring sag you should do it without pump connected. If it’s losing air when riding then more likely seals or valve. Or are you pumping up, then on re-connecting pump it’s down again? If so, you lose pressure just by connecting the pump.