Take the belts off. Turn each pulley and tensioner by hand. Does yours have the air dam installed under the bumper? If not, remove it and check the power steering fluid lines. Check the transmission oil cooler lines. Unfortunately, there is not a transmission oil level stick. Only a plug. Eliminate the easy stuff before taking it a shop. If the items mentioned are good, have it towed to get the transmission oil level checked. The key is to find the liquid leak.

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'06 X5 3.0i - bought @143,123 miles (12/26/20)