In the past I have sometimes restored an aluminum part to a healthy shine by removing the anodizing first with 220 wet dry paper. Next I go to 400 then 600 then 1200 then 3m compound. I haven't seen an negative effect to doing this yet. You can even get a satin finish by not using the compound as a last step. This begs the question... What is the disadvantage of doing this other than making an original part, unoriginal? What was the original advantage of putting an anodized layer on in the first place. I have found that a horribly scratched seatpost or stem or brake lever is completely usable and attractive after a 30 minute process.
Garth Libre in Miami Shores Fl.