2006 X5 Blowing White Smoke

I own a 2006 X5, 4.4i, 79,000 miles. I am the second owner, purchased it with 19K miles on it two years ago. Several weeks ago, the car starts blowing white smoke out of the tail pipe. I does not happen all the time, but at least once a day, typically at start up and goes away. On occasion during driving, typically at acceleration, a clicking sound will happen and smoke will blow.

I took it into a BMW mechanic who tells me the valve stems are gone and need replacing. He says its a major deal costing upwards of $3K if it can be fixed. He however, does not seem confident it can be fixed and thinks it may need an engine replacement.

Someone out there must have had this issue before me with theirs, can you tell me what you found and how you fixed it? Its hard to believe a 2006 with only 79,000 miles needs an engine replacement.

Thanks.

Phoenix BMX X5