someone recommended these guys http://www.dupageautowerks.com/webpa.../homepage.html
I don't have any knowledge about them, just someone else's recommendation.
You want as much fuel lubricity as you can get. Supposedly biodiesel dilutes the engine oil, if it were my car I'd try B11 and do some oil testing from some place like blackstone to monitor engine oil. http://www.myturbodiesel.com/1000q/D...AQ-VW-Audi.htm
read the DPF FAQ for some more info on this issue