Its not your valve stem seals. Its sludge in your engine causing oil to be sucked back into the cylinders. That white stuff you saw? Well its all in your valve covers. Its blocking the flow of air and causing oil to be sucked right back into the engine. Dont worry, its common. All too much so due to BMW recommending 15000 mile oil change intervals. Oil breaks down, yes even synthetic oil. Do not wait 15000 miles to change your oil. Start there. Use Mobil 1 synthetic European Formula. You can use an oil flush if you feel comfortable doing it. Lubri Molly is what is recommended. Your ccv valves were the vehicle not the culprit of your problem. You are driving short distances usually??

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2006 x5 4.4