I just purchased a 2013 E350 Bluetec so now I can update the info I gave in post #6 above. It has the OM642 (V6) and the AdBlue tank in the trunk. In my search for a new vehicle I discovered that the transition year to the OM651 (inline 4) was 2014 not 2013.

Originally I had the year wrong on the sedans. I pasted and edited the statement below. Edits in bold text.

They transitioned to the W212 in 2010, and these models were equipped with DEF. AdBlue tank in the spare tire well.
I think when they did the refreshed W212 in 2014, they figured out how to move the DEF tank out of the spare tire well. These can be had up until 2016 which was the end of the line for the W212. The refresh models 2014-2016 are the OM651 4-cylinder twin turbos.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech