Are you sure they are aluminum and not chromed also
? Alot of those rocker box covers are chromed pieces, and they will pit just the way you are describing. I really can not tell you if they are or not, without messing up the chrome (if it is chrome). the pits you are describing may just be badly corroded chrome plating that is now gone, leaving the pits behind. Also, could be as you described and be porosity though, I can clearly say that Harley parts are usually no where near the quality of a Jap bike in terms of lack of porosity in a cast aluminum piece. Jap bikes are far easier to polish than a cast (probably in china) harley piece.