2008 x5 4.8 cylinder head crack!

[LA08X5]

This one is strange.

I have a 2008 X5 with 64k miles. There is a small hairline crack on the left cylinder head. The car has not overheated and drives fine, but the crack seeps oil after the engine is turned off. It took forever for my indy mechanic to find the crack, because it's not visible with the naked eye and it does not seem to leak when the engine is running. The oil begins seeping about 30 seconds after the engine is turned off. My Indy mechanic thinks it's a manufacturer defect from when the head was forged.

A side note... Just before the warranty was up last year, the BMW dealer replaced a leaking valve cover gasket on the same head... Then this summer, after the warranty was up, my Indy said that same valve cover was leaking again. I took it back to the dealer and after some wrangling, I got them to redo the valve cover gasket again under a repair warranty... but they also replaced the timing cover seals which cost me another $1000!

Now we discover this hairline crack in the cylinder head the dealer had worked on twice.

I've had no problems with over heating and there is no coolant leaking into the head...only oil slowing seeping out after the engine is turned off.

This is going to cost thousands to fix!

It's back at the dealer now and I'm wondering if this crack could have been caused by them?

So my question is: when replacing the valve and timing cover gaskets is there something the mechanic may have done to cause the crack?

ie: over torquing bolts or tightening in the wrong order.

I'm trying to learn as much as I can about what can cause this sort of thing before the dealer tells me it's not their problem.

please see attached pics