Use the cheapest oil you can possibly find; it will not be synthetic. No complaints here with a mk3 TD and I drive it like it's stolen every day hahaa proving that synthetic oil doesn't do noticable shyte for anything.
Ok fine I meant cheapest oil that says diesel on the container somewhere. and, NO I don't moniter oil temp or do oil samples or none of that; sure the benifits are obvious when you look at a piece of paper... but my engine still works just fine and when/if it blows up or starts to smoke, I sure as hell will not blame it on oil... unless it runs out of oil completely.