Originally Posted By: sloinker
High mileage 1.8L VW engine with 5-6k OCI is ripe for a VVT actuator failure and is probably one mass of sludge already. Since this car has a small oil sump and small filter the 5-6K OCI has ruined a lot of these engines, even with the updated only synthetic recommendation. As pointed out there is no M1 AP in 0W-40 and rather than using a class III castrol or M1, reach for a synthetic that has some measure of PAO and/or esters. Find some Ravenol, Motul, Amsoil, Red Line etc. In an appropriate grade/weight specification or continue using the class III and listen closely for when the VVT actuator starts making chain slapping noises at low rpm's and replace it. Come to think of it. The application of a true synthetic may break down the existing inherent sludge and cause catastrophic engine failure. Use the castrol and let sleeping dogs lie.
Lot of opinion in here.
Run a quality synthetic with 502 approval. Many 502 oils also have BMW LL-01, MB 229.5, and Porsche A40 approval. I would choose an oil that meets all 4 to ensure you are getting a certifiably quality oil. There’s a few readily available to choose from.