With my father's purchase of a 2004 Mazda Tribute, he was giving up his old workhorse, a 1998 Jetta TDI. I (gleefully) took it off his hands. Currently has almost 196,000 miles and still going strong (still the original clutch too, which sometimes scares me... but I am assured the car had more freeway driving than anything else. It does operate ok).
At first he would take it to quick lube places and get god-knows-what in it. Until once they failed to properly fasten the plastic underbody shield and it began to drag underneath the car and get chewed up. After that he did the oil changes himself (and when I started working at a tire shop doing oil changes and tires, I began doing his oil changes... and of course now that it's mine, I still do them
). He was recommended to use Delvac 1300 by someone who owned a diesel truck. He has been using it since, as have I.
Never had an oil analysis or anything. I am fairly new to this, but I have taken a great interest in oils lately. I want to find out what is the best for each vehicle in my family, as I seem to be the one taking care of all the vehicles these days.
I have not seen Delvac 1 in local stores, unfortunately. Delvac 1300 is readily available, however. I have been researching into products like Amsoil's Series 3000 5w30. Although stumbling across this messageboard appears to be a blessing. Some very knowledgeable people around here who have been there and tried that. So I'm not getting biased information from the one of a bazillion Amsoil dealers on the internet... heh.
In short, I would love to hear what comes most-recommended for TDIs and the reasons behind it. One of these days I'll send in an oil sample for analysis just out of curiosity.
I am also considering by-pass filters as well. There's so many things to do!