There's a fairly big discussion about this over at the TDI forum. According to the so-called Spicer Diesel Additive Test, SuperTech ashless 2-cycle oil from Walmart beats many diesel fuel additives when it comes to lubricity. It's better than PowerService for example and about the same as the Amsoil diesel additive. I'm currently trying it in both of my cars. Initially I had some injector knock and hesitation probably due to insufficient mixing, but it quickly cleared up and returned to normal. The engine sound is perhaps slightly quieter now, but it's not a big difference and a cetane booster would probably do an even better job in that department. No other noticed change thus far. I haven't had a chance to evaluate mileage yet.

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2004 VW Jetta TDI (manual)

Past MB's: '96 E300D, '83 240D, '82 300D, '87 300D, '87 420SEL