Fan Shroud Restoration

Here's a question that I hope someone might have a solution to.

I have an old fan shroud that is faded and oxidized. I've cleaned it with 30% vinegar to get some of the oxidation off, but it's still that chalky grey color. Not as bad as when I started, but still looks bad. I've tried using Mothers Back to Black Trim & Plastic Restorer, but as soon as that stuff dissipates, it's back to where it was. Even tried scuffing that stuff in with some 2000 grit sandpaper and it does nothing.

I've read on the internet all sorts of fixes from peanut butter to petroleum jelly. There's also a thing going around on the intertoobs about using a heat gun to pull the oils out to restore it. But I feel that'll only weaken the plastic and make things worse.

Has anyone found something that works to restore it back to how it looked when it was newer? I don't want to paint it. There has to be a method to this madness. I appreciate any advice anyone can give me. I'll give anything a try if it'll work.

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