You can get proper polishing compounds for aluminium/alloys. It comes in solid blocks. Use this with a buffing wheel on an electric drill.
I had a catologue listing various types of compound but I can't find it at the moment. I once bought a block from a shop that mainly dealt with polishing stones & gems, but it was for alloys. It worked a treat on the dull alloy castings I had on a kit car I built many years ago and they never corroded after being done.
freeservers keep putting up a can't link message in place of my pics (this is a new thing). it looks quite...errr...funny
unfortunately, shugs avatar comes from the same site. i sometimes have to open up the pictures in my browser to get them to work.