Don't want to take this thread off topic, but I just replaced that heater valve assembly in my 2005 albeit for reasons other than what you mentioned. I am curious how a leak within it can cause coolant to enter the intake though.As for the smoke, check if you are losing coolant first. Before condemning a head gasket, check the dreaded heater flow control assembly. My current 2002 project had the seal in that valve leak and send small amounts of coolant into the intake resulting in white smoke from exhaust. Pain in the *** to get to and replace, but still easier then an unnecessary head gasket replacement.