Or just buy 5litres Quantum Longlife 3 which is VAG’s own brand. I never extend oil changes out to c18k or 18 months, but change it annually if you do an average mileage.
Quantum is available from a number of reputable EBay sellers. 5 litres will allow you to have enough ‘top up’ oil for hopefully a couple of years.
Regards,
Gareth.