Looks worth trying. I've found UPVC window frame cleaner(available from double glazing suppliers) really cleans the plastics up well on white ones. It doesn't remove deep scratches but it cleans off ingrained dirt in them.
here is a tip i found that made mine look like new. get a heat gun and run it lightly over the plastics (not near graphics) it slightly melts the top layer of the plastic and helps reset it, really helps around bends where the damn white marks appear. i mixed that with some light sanding and it worked brilliantly. just a suggestion.
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