So, I finally found where the oil in my coolant was coming from...the transmision oil cooler.

Got a new trans oil cooler installed and just as I was about to drive off, the lower hose decoupled from the cooler! Lucky the car was stationary, we shut her down right away. Spilled a liter or so of fluid.

Taking a close look at the quick coupling, it seems the hose coupling has a series of spring clips in its mouth that engage a raised flange on the oil cooler tube.

My indy connected them again and put the front of the car on stands to observe. We put the car in reverse and drive multiple times and the hose didnt shift or leak.

My indy recommends replacing the whole hose to be sure.

Are these quick couplings a failure point on these hoses? Do they fail and allow the hose to separate from the cooler?

Or was this improper install by my indy? A part of me thinks he may not have had the coupling fully engaged and so it decoupled with the additional line pressure of shifting into gear.

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04 X5 3.0i auto
03 X5 4.6is