Also not the most water resistant. First rainy day will pretty much wash it all off.Apparently I'm in the minority here but I wouldn't use 303 on that. I used 303 on one piece of exterior trim on my Ascent and have regretted it since. Now that piece almost looks like it has an oil sheen over it. 303 looks great but you'd have to keep applying it to maintain that. It does work excellent on the interior.
Any guesses what the drip marks might be from? My trim has greyed some, though not as fast as me, but it doesn't have those streaks in it.
I'm not sure what some people have used on Chevy Avalanches, but if you ever see one with all the plastic that looks nice ask them.