ATF cooler BMW X5 E53

[Johnoc70]

Hi. I need your help again. I went to top up my radiator coolant on my X5 E53 3.0i and found some oil in the expansion bottle. The car is running fine and not overheating so I’m hoping it’s the ATF cooler that’s leaking ATF in to the cooling system. What’s the easiest way to confirm this.

Thanks

[AW10]

Some oil... can you quantify this?

Any mayo on the underside of the oil filler cap?

[Johnoc70]

Hi. Seems to be small bubbles of creamy substance in expansion bottle. No mayo on oil cap filler but oil level a bit low. Doesn’t seem to be any oil in engine oil. Can’t see anything on dip stick