That is old brown rust with pitting. The axles are likely rusty too, and the collectors.
If at all possible I would pull the wheels to get at all the corrosion. I broke an axle the last time I did that. C. W. properly admonished me that I should have soaked it in penetrating oil for a day or two. Instead I was in an all fire of a hurry. So take the education, Sunrise, without paying the tuition.
Then soak the wheel in E - R for a full day.
