head gasket is good dont worry .
oil cooler on the engine , make sure the new cooler has a new profile gasket
also dont over torque the bolts when refitting , if possible get new bolts from bmw .
flush the water out thrice
and remember these coolers hate water ! when you refill the cooling system you need minimum 50% coolant (anti freeze) .
i did mine a year ago d.i,y