I run Diesel Kleen from time to time, seems to help clean out the fuel system as it advertises. Power Service (its manufacturer) sells it super concentrated in 2.5 gallon jugs, treats 3750 gallons for around $120, making it around $.03 to treat one gallon. I'm considering buying one of those jugs then divvying it up to run it every tank.
I also believe in the power of diesel purge, after running through 75% of the 2 cans I put in my 190D. The remaining purge was a dark, murky grey color, when it is originally clear and an amber color.

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Current: 1975 450SEL, 83 300D, 88 Yugo GVX, 90 300D OM603 swap, 91 F150 4.6 4v swap, 93 190E Sportline LE 3.0L M104 swap, 93 190E Sportline LE Megasquirt, 03 Sprinter, 06 E500 4Matic wagon.