I personally haven't tried this, but it sounds good, and these folks are typically very good with their advice.
Recomendo
November 17 · Issue #174 ·
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A weekly newsletter that gives you 6 brief personal recommendations of cool stuff. Check out our 2018 Recomendo book:
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Plastic restoring gel
Old yellowed plastic looks unrecoverable but it can be magically brought back to its original whiteness or bright color using hydrogen peroxide gel from a hair salon. The gel prevents the concentrated hydrogen peroxide from slipping off; you also wrap it in cling plastic to keep it moist. Plenty of YouTubers demonstrate how they restore old computers, old toys, old appliances with this stuff. I used
Super Star Cream Peroxide to bring back white plastic parts in our bathroom. (Also good for whitening old bones.) — KK