I have a 2002 GMC 2500 HD 6.6 L Duramax Turbo. I have been losing coolant for about a year and now it is getting worse. It is about a half gallon per 100 miles. I have not found any drips on the ground. I can smell it in the engine compartment. There is no coolant in the oil. I heard that it could be the injector leaking internally. I also heard that on the right hand side there is plate between the transmission and the block that can leak coolant. The right front head gasket in leaking externally very little. To me, it does not explain where all coolant is going. I am thinking of tearing it down to replace the head gasket. Do you have any suggestions on what else I should look for internally while it is apart?