2005 BMW X5 BMW Whilte Smoke

2005 BMW X5

Ok so I am thinking the head gasket is shot. Here are the symptoms:

1. Excessive white smoke from the tailpipes especially if the car sits idling for a few minutes and you drive away.
2. Low cylinder compression on cylinders 4 and 8 show 35% leakage with the air pressure leak test.
3. Visible scoring and pitting on the inside of the cylinder 4 & 8 walls.
4. Oil usage very high over the last few months.
5. 150K kilometers on the odometer with the 160K BMW Certified Warranty package.

The dealer would like to bring my X5 4.4i in for engine disassmbly to confirm the issue and support any warranty claim. They are already recommending engine replacement but need evidence for the case to present to BMW. They warned me up front that if whatever the issue is that if warranty does not cover the damage then I will be on the hook for the disassembly hours and either the new engine or putting the old one back together.

Please anyone provide your thoughts on what the problem is with my X5.

Thanks in advance!