Did that O-ring replacement with the engine out and remember thinking that that would be a job from hell to do with the engine in the car. I just spent another two hours under there to insert the spacer in my front drive shaft and if I had to do that O-ring swap, I think I would either lower the sub-frame or pull both radiators and the PS pump. Neither is ideal but lowering the sub-frame at least would allow a view of the offending items.

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2003 4.4i black ext./black int./black headliner (kid's runabout)
2014 535d X-drive, M package, silver/black interior

Sold but not forgotten:
2009 E70 35d, black ext./black int./black headliner (sold 2021)
2006 4.8iS Le Mans blue/cream int./black headliner, SOLD in 2012 sadly...

Other hardware:
2015 Cayenne S (wife's new DD and definitely wroooommmmm)
2016 Tundra 1794 edition crew cab, luxo hauler
2005 Tundra crew cab, weekend hauler. Sold after 150k very happy miles.