A battery warning indicator on start-up prompted me to start checking the battery and the charging system on our '07 X5 4.8 with 90K miles. The 2 year old Interstate battery (not AGM) was pulled and tested good, so the alternator was the next suspect--it had stopped charging. My indie and I worked together to remove the Valeo alternator, which is literally buried at the very bottom left side of the engine. He then sent the alternator in to be rebuilt by our local top-notch independent alternator/starter specialist. They had the alternator done and like new by the next day, however they said upon return that the alternator had failed because it had been contaminated by oil (or antifreeze?). Apparently there is a membrane between the aluminum housing and the voltage regulator inside the alternate that gets soaked with oil and causes failure. The usual culprit for the oil leak is a hose connection housing for the oil cooler/thermostat on the engine block directly behind the alternator and power steering pump, it is in a spot almost impossible to see. The dealers a very familiar with this issue, there is a $5 gasket that fails. Upon close examination in this case, however, there is no sign of an oil leak from there, it is clean and dry, so the oil contamination must have been from a formerly leaking coolant expansion tank, or possibly now from the cam position sensor directly above the alternator could be the problem? The rebuilt alternator is now back in the car, waiting for a new serpentine belt tomorrow to complete the job. If anyone is considering this DIY alternator R&R, there are few tips I can provide.