What clear coat are you using? There are a couple of aluminium-specific clear coats out there. AlumaClear (not sure if it's available in Oz) and Protectaclear. But looking at your aluminium polishing thread, I'm sure that you already know about these products.
www.everbritecoatings.com.au

Restore & Protect Aluminum to Look New for Years | Everbrite Coatings | Australia
To make aluminum surfaces look brand new or stay looking new, use our coatings to protect your surfaces from fading, oxidation and corrosion. Our coatings are easy to apply, scratch-resistant and clear, to make your surface look smooth and shiny. For architectural metal, use Everbrite. For...
