My 2005 K74 has started to get bubbles in the expansion tank, the tank also fills up above the top level. I've change the EGR unit, thermostat, and radiator cap. My next move is to remove the head, before starting could there be anything else to check, and when the heads off will the crack in the head be visible or the head gasket show signs of leaking. Finally would it be wise just to buy a new head and gasket set and be done with it.

new head and be done with it gets my vote