E-mailed marketing.airlinepartnerships@europcar.com as others have done and included screenshots of Hertz Five Star and Sixt Platinum memberships and had one reservation already. The issue with my Sixt Platinum, according to Europcar, was that it has no expiry, permanently linked to my SAS EuroBonus Gold-for-Life and same for Hertz linked to Accor Gold (screenshots for both included in later e-mails), which Hertz seems to consider permanent. Short of the long, landed at Europcar Privilege "Level 2 - Traveller" (2 of 4) and not higher, as I had hoped. Took a week or so.