The six series currently does have a diesel, the 635. I just read a review on it. It probably wont come to the states though, so you are right on that front.

The review kind of hinted that it wasnt the best chassis:engine match.

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93 300D 2.5 Turbo, Black/Palomino 273K
09 E350 Black/Black 41K

Just saw a 635d pulling away from the Hotel Bristol in Paris the other day..man that is a sweet ride, and it was dead silent at idle as well. No idea how it drives though..a little to rich for my blood

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1982 300TD 210K miles ("The Replacement" aka "The Anvil") - SOLD
1979 300SD 245K miles (never ending project)
2007 Pinarello F3:13
1995 Ducati 916 (SOLD, sniff)
1999 Ducati 900SSie (SOLD)