I used to not believe in additives. Cummins has an issue with Bosch injectors in the '07 and above 6.7 L B series engines in Automotive applications, like tow trucks and yard goats...that's the only vehicles we have seen problems in. After 4 SETS...24 new injectors, there was a Ford F650 roll back that came back pushing black smoke thru the DPF and knocking on acceleration. I figured the factory was just gonna throw more injectors at it since Bosch engineers had been out on at least 6 other vehicles, saw what they were doing, but still can't figure out what was/is wrong. A Cummins engineer called me and said he was sending a "special" additive to me and said to put 3 oz into 50 gallons, then run the pizz out of it on the dyno. Turned out to be a Valvoline product...i'll get pics tomorrow...The engine was blubbering and smoking and knocking real bad, thought it was gonna hole a piston, then, all of a sudden, it cleaned up. Ran great, good HP and no more knock/smoke. Put a new DPF on it and shipped it. it has not been back. At the time of the 5th failure, it had around 10k on it and had a date in service of around Feb. 2008. I might try some of that stuff!