Once the corrosion has gone under the anodizing layer and actually caused pits on the aluminum surface, you will have no other option than to polish it out using polishng compounds of graduating grits (that will remove the anodizing) till they are mostly gone. Please note tht you will be removing metal from the bike with any kind of abrasive polishing you might use, but a few micronsof metal off will most likely never be noticed. If the pits are very deep, you might have to just live with them and hopefully the poished surfaces around the pits takes attention away from them.

Chombi