#4 0000 Steel wool and Semi-Chrome polish work well. I believe Aluminum oxide forms after reacting with water. It is not too hard to keep it looking good and bright, but I would not polish it to a high luster finish as that would drive you crazy trying to keep that look. I find old cotton shirts work best, but must be thrown away after a couple polishes as the rags become too black to use on anything else. That oxide forms in your chain adjuster bolt holes also, so remove them and put on anti-sieze compound so they don't freeze up.
Sorry if there is any misinformation here.. someone will straighten it out, I'm sure