Leaking Coolant-Goes into the Valley of the Engine

What is your question?

My van has been leaking coolant for over a year now. We have taken it to 3 mechanics. The first mechanic replaced the intake manifold gasket which did not work. It continued to leak fluid. He said it is an external head gasket leak. But when pressure tests it is ok. The second mechanic couldn't find leak. The third mechanic they did pressure test and couldn't find any leaks. It is leaking because I smell it and I have to replace it it the container at least 1 x per week. We find it in the valley of the engine. Could it be a small head gasket leak externally? Any help would be appreciated.