just as info, wifey Liz's lil Zr has plastic lens and being an 04 plater , its the same age and sits out in all the same weathers as the ZT's.But to date the lens are still pefect, not a spec of discolouring
.
The 06 1.8T mk2 's lights are awful after a year or so since a polish session, the Mk 1 CDTi's are due for a clean as just one side has gone off since a polish a couple years ago.
And the Mk 1 260 lights , again an 04 are still very good and never been touched
So no rhyme or reason or nor particular model to blame
So must be the plastic type and the makers !
C