We know that UWL will not 'stain' trim etc. So last fall (late Sept) when I was getting the truck for winter, I thought, "Let's try this on the mirror heads."
After waxing the body, there was a bit of product still on the pad. I just 'zoomed' over the plastic (textured), wiped it off and called it good.
Fast forward to yesterday (14Mar12), I was able to give that big sucker a 'proper' wash (70* in Mn!)...the mirrors look like they did in Sept. Whereas the bumper covers, also a textured plastic, well they look like black does after a winter. Kinda dull and faded.
If this will work on ALL black plastics, I do not know. But on a 2004 Chev 2500HD it does.