Broken Exhaust VANOS bolts
I have a 2011 E92 Xdrive and had an issue where the "Service Engine Soon" light came on. Took it to the dealer and they ran the code and diagnosed VANOS issue. The dealer replaced the solenoid valve and sent me on my way. The next week, the light returned so I took it back to the dealer. This time they discovered that the exhaust VANOS unit had three broken bolts. They had to remove the exhaust camshaft to retrieve the broken bolts. They ended up replacing both VANOS units and retiming the engine.
I was lucky because the car warranty runs out in less than 800 miles!! I wonder what this would have cost if not covered by warranty?