Polished aluminum trim coating

Irregardless as to what you call it, the O.P. wanted to know what to use to protect his polished aluminum parts. Clear anodizing is the best way to protect those parts. It is quite impervious to common automotive chemicals, and a simple coat of auto wax will keep it clean & shiny almost forever. If you send aluminum trim out to a restorer such as "King of Trim" they will clear anodize the parts after polishing, and then apply any paint details last (as needed). The stuff I had done 10+ years ago still looks brand new.
There are many drawbacks to all other coatings. Any type of clear paint will change the color of the aluminum slightly, as well as almost always dulling the shine somewhat. They tend to flake/peel off too, mostly because in order to get paint to "stick" to metal it needs to be roughed up somewhat. Of course you cannot do that to polished parts.