hello all I just wanted to share a repair I successfully performed a few years ago and still going strong. A few years ago I had a coolant leak from the back head of my GM 3500 (3.5) flex fuel from my 2007 Monte Carlo LS. I couldn't find the leak and so brought it to the "experts" at F___stone whom pressure tested it and in their great wisdom said it was the head gasket. I had my doubts and bought a mirror to actually find the leak myself. I discovered this coolant crossover pipe gasket was the cause of the leak (back head front of the motor) and went to a Chevy dealer to buy the new gaskets. The Chevy dealer service department didn't even know what it was and I had to explain to them via diagram what I needed to buy. They later did print out the diagram for me which actually helped. In order to change these gaskets at the front of the motor you need to remove the alternator, power steering pump, heater hose lines, filler neck for dexcool and several bolts across the crossover pipe itself. I am attaching a diagram and pictures of the blown gaskets. I will also include a TSB for this issue. The coolant crossover pipes vary from year to year as the design changed. This is shown in the TSB. If anyone has any questions feel free to post them. I hope this helps someone and they too avoid changing their head gaskets

! It was very hard to find where this leak was coming from!