I've had pretty good luck with Motul's Wash & Wax and Shine & Go. They are products designed for motorcycles and you can pick them up at motorcycle dealerships. They are supposed to work equally well on metallic and plastic surfaces. You spray on the Wash & Wax and leave it on for a bit then wipe it off and it leaves the cladding a nice dark color. Shine & Go is more for touch ups and you also spray it on, but you just leave it. It gives a sheen to the cladding that some like, but if you want a less lustrous look you can wipe it off.