check the users handbook; it identifies the permitted oil standards for longlife service, and for fixed-interval. See also the following thread where I put the info from my B6 S4 handbook:
http://www.rs246.com/index.php?name=PNp ... w=previous
This talks about "multigrade thin-running oil VW 503 01 or VW503 00" which refers to a VAG code you should find on the small print on the back of each oil bottle in the shops; you should also be able to find it if you search for the oil specs on the company web-sites or wherever (try googling for 503 00 ??)
Only thing is; the handbook for a B6 was written some time ago and since then VAG have changed/ improved their standards. It's entirely possible that you can use the new standard oils as well (ie I would guess the new VAG standard for a B7 longlife would be OK for a B6 ?)
I did use Castrol SLX Longlife II but in my Halfords it seems to have been superseded by something else. Audi used some Shell Helix xxx at the last longlife service....., dont know what exactly
