Correcting Stained Paint?

[Setec Astronomy]

Surface rust on plastic/ABS?

Ha, excellent point.

To the OP: Clay is only going to do something if that stain is above/on the surface. If you can`t feel it, and since you`ve already marred it with the clay, it would seem appropriate to try some polish and see if it does anything. The problem with staining is that is can sometimes penetrate fairly far into the paint.