The photo posted above looks just like the blockage in my 1998 ML320's EGR tube. I removed, cleaned and replaced mine today. The check engine light went out (after three engine starts and not detecting the fault). Mileage is at 190,500.
Thanks for the detail in this thread. It was a big help and good supplement to the WIS info.
Ken

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2014 E250 Bluetec 4-Matic
2014 GL350 Bluetec 4-Matic
1996 Chevy Tahoe 4 x 4
2009 ML350 (sold)
2005 SLK350 (sold)
1999 E300 Turbodiesel (sold)
1998 ML320 (sold)
1991 300D 2.5 Turbodiesel (sold)