Use Kreen 500 miles before your next oil change, I did that both in my tank and engine on my OM606. I just can't brag enough about Kreen, the injector knock were gone and the oil (drained) came out like gooey tar.

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06 MB E320 CDI 123k miles
14 Sienna (wife's DD) 36k miles
11 GL350 Bluetec 136k (Sold)
96 E300; 292k+ miles (Donated)
11 Sprinter 22K+ miles (Sold)