What is more important...having an oil that meets the VW 505 spec or meet the CF4 or CG4 spec (both called for in owners manual)? I've used the Delvac 1 oil but it is harder to find near my home (~100 miles to store). I've also purchased Castrol TXT 505 01 oil from the dealer (have to go from 8 to 5 Monday through Saturday). I've been looking to buy the Mobil 1 5W-40 Truck & SUV but I haven't found it in my area. The Castrol is probably the best match as it states it was made for the TDI engine. I picked up 6 qts of the 0W-40 at Checker tonight because it was handy. Anybody have any input? Stick with the 0W-40 or go back to the dealer for the Castrol?