Can I fix a leaking Pressure R. Valve?

I have this pressure regulator valve that I believe is leaking from the spring disc. Is it possible to fix this by removing the nut and bolt and applying some kind of putty or paste or replacing the disc with a repair kit or are these things not meant to be repaired but just replaced? And how would I remove it? Its attached end to end in the drywall.. :blink:

Thanks :)

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