Easiest 5-minute fix to yellowing headlights we found was:
- Wash and rinse headlights
- Meguiar's Ultimate Polish" using a microfibre towel.
- Apply some wax or other protection

Note that above products may not be appropriate for the polycarbonate lenses so read the label. We had no issues but you might.

We have tried several popular retail UV restore kits (basically sandpaper, polish, protectant). They took a lot of time and work. Not sure if the "Meguiar's Ultmate Polish" trick would work if one had not previously sanded the headlights (we sanded them years ago but not for this 5 minute test)..

None of the headlight "restore" products or tricks lasted us more than say 6 months (car parked inside or facing south might have better success)..

We read about pelople using other "tricks" like WD-40 or toothpaste. None of these "tricks" worked on the Astra. Maybe they are great for headlight cover plastics/coatings on different car models.

 

I used Maguire's Plastix (same product?) on the headlights for my 97 SC2. I did not wax them afterwards, as it appears I am a moron in this respect. I did not sand prior to application. The outcome was awesome, but without protecting it, it would again become yellowed in about one year..

 

The protectants we tried just didn't seem to last very long.

Maybe a 2K clear (dangerous to breath in) or some other pro application would be more durable.

 

Not quite fix it in a can, because it's more expensive, but the same concept.
Polishing away the outer oxidation layer away doesn't stop whatever layer you get to from then oxidizing due to the UV of the sun and other factors.

The true cure probably eats away the lining of your lungs and causes permanent neurological damage. This would leave you unable to breathe and likely unable to drive. Clearly a lose-lose

 

I have used baking soda on a damp cloth. It's okay for a temporary fix, but nothing that I've tried from the auto parts stores has lasted longer than 6 months. Sometimes I miss the days of glass headlights.