Our family has an `04 Jetta TDI PD that we have been running the Castrol TXT 505.01 oil from the dealer for now 39k miles. I've been searching around and found ELF 5w40, Motul 5w40 and Pentosynth TS 5w40 to all be in the same price range as the Castrol TXT. Out of all those choices, which would be best to pick? I know of the new ELF 0w30 but it's rather pricey at $16.50 per liter. Thanks for any help.