Guys - I posted a reply to Ivo's question in more detail on the tech tips area - but i'll reiterate. Check out
www.stanadyne.com
and get some Performance formula. They manufacture diesel fuel systems/pumps/injectors and know diesels really well. Many additives are just marketing hype. I've heard good things about redline dfc as well. Stanadyne was just fully endorsed and recommended by VW in their technical bulletins. I've used it in my car with no complaints. The stuff is very concentrated, just a few ounces(easily measured on the bottle with the little lines) per fillup -
Make sure your additive does NOT contain alcohol, and don't put ATF in your fuel -
hope this helps,
Dave