where is the cause for cooalnt leak in rear center of 3.5L engine

https://www.moparpartsoverstock.com/showAssembly.aspx?ukey_assembly=896944 Pressure test the cooling system and watch these components. One of those is most likely leaking. You can use a UV dye and UV light to see the leak as it happens as well. No need to wash the engine first with UV dye, just don't spill any. You'll hear the leak when it is pressurized either way. Good luck, and happy hunting.