I have bought this foam rubber, cut it to the length needed, clued the ends together with superglue and fixed it in the window groove with contact adhesive. For the different portlights I have used 10 mm or 8 mm diameter foam rubber.
https://www.gummiprofile24.de/epages/64048014.sf/de_DE/?ObjectPath=/Shops/64048014/Categories/Produkte/%22EPDM%20Moosgummi-Rundprofile%20schwarz%22 -- Gerhard Mueller Amel Sharki #60 Currently Kalamata, Greece
