Greygate polish is brilliant for rear screens.
It is used by NASA and BT (and me) so must be good,
2 bottles cost me £7 from eBay, I only used a 1/3 of one doing both sides of a heavily oxidised screen.
It also works well on plastic headlights.
Home to black Alfa Romeo 159 3.2 V6 Q4 ,green MGF VVC and red MG Maestro T16.
MG - the friendly marque.
