Hi.
I have restored lights. rub them down with 2000 wet and dry then polish them with compound off ebay, it is called 'Lamp Doctor'
https://www.ebay.co.uk/itm/K2-Pro-LAMP-DOCTOR-CLEANER-RESTORES-POLISH-YELLOWED-SCRATCHED-HEADLIGHT-LENSES/291952967242?epid=3032793183&ha
Regards,
Richard.