Buy the way you can buy the full gaskets for the C pillar air vents?
https://www.ebay.co.uk/itm/Mk2-Cortina-Rear-Pillar-Vent-Seals-GT-Lotus-Savage-1600E-Super-De-Luxe-Brand-New/201548271599?epid=1875104584&hash=item2eed368fef:g:RmgAAOSwZtJW9DS2
Very nice MZ as well I had one as my first transport in 1987