FYI, the drain plug on an '06 V8 4.8is is on the driver's side of the bottom of the radiator. The plug is blue plastic, and you need to take of the front section of the under chassis engine cover to access it.

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'06 X5 4.8is, TiAg/black, cold weather pkg., comfort seats
'07 750Li, TiAg/black, sport pkg.
'05 Ford F350 silver met./slate gray, Lariat, 6.0 PSD, CC, DRW, FX4