Usually it can not be repaired... no way. It is anodisized alumenum, a invisible spot repair is impossible. Grinding on a spot will always be visible, more or less.
If the panel is flat and has no text or printings on it and has no direct contact to other panels, it can be brushed in total, the complete surface.
But even then, there will be a slight difference to the original surface, colour and gloss. And a new anodisizing is pretty expensive... clear coat can do it. But in total i would do this only for parts, that are very expensive or not available anymore.