I’m stuck.

The MAAS took off a lot of the black discolouration, but I’m not making any further progress with the really black spots. They aren’t pits - I can’t feel any difference in height between them and the surrounding metal.
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I’ve tried using 600 grit wet/dry, but it did not seem to have any effect. Any suggestions before I plug in my Dremel and start using the Scotchbrite wheels?