Bubble magus 7 skimmer corrosion?

[Tyler Flynn]

Cleaned my skimmer today and found that the rotor is covered in black residue. I’m assuming this us magnet corrosion?

Will replacing the rotor assembly be enough? Or should i be looking at replacing the pump?

 

[blaxsun]

What does the inside of the pump look like?

 

[Tyler Flynn]

What does the inside of the pump look like?

Pump looks ok. The black gunk cleaned off the inside using q tips.
i dose nitrate and phosphate so the main loss on my skimmer being down is gas exchange for ph