Quote: Try some of BadThad's VerdiCare on the obverse.
I try not to use VC on toned coins, especially on ones like this, it can negatively affect the toning. Thin film interference is very sensitive and easily impacted by anything that alters the light refraction.
Also, it's not active corrosion on the obverse IMO. The black stuff appears to be organic in composition. I like it there, shows the originality of the surfaces!