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.
just had my water pump changed and the vw techie advised me to change my oil filter to a genuine one as it has a return valve thing. i got some castrol magnatec for £12 (approx $6) from Asda (Walmart) and have used that. car isnt drinking any oil or anything. gonna visit the derv doctor in derby as my boost is a litle low, running at 0.6 bar insted of 1.2 bar.
The Uni of Technology in QLD performed an independant International Standards Falex test on a wide range of oils including Mobil 1, Valvoline and Castrol oils. They also did the same tests on oil additives put in to oils. The test measured the point at which the oil loses friction and fails to lubricate the moving metal parts. In the end Mobil 1 which was one of the top performers failed at *2250lbs of force. Actually it is interesting to note that Mobil 1 and a Wynns oil additive actually did worse at a reading of *2000lbs of force. The worst performers was Castrol Magnatec which failed at *750lbs of force.* figures taken from an article in the magazine "The Jaguar" edition 107.