I found recently a research made by german institute (engine developement) and they refering to bad influence on diesel engines caused by modern specs diesel fuels. Actual fuels are less "greasy"because of sulph lack. At the end of the research they say that the only improvement can be done is to mix diesel with 1/200 2t oil. It maintain a cleaner fuel system, reduce fumes, compatible with catalitic converters and PF, and not the least, a 3-5% fuel economy.