I have a 2006 stock Duramax. Started leaking antifreeze from bottom of head on passenger side. No water in oil, no white smoke. I've looked all over top and can't see a leak on top, only on bottom. Had the system pressurized and it held 15psi. There hasn't been any blow back from the reservoir and the radiator hose does not get hard. Toook it to mechanic and he says it is a head leak. I've also notice that the heater hasn't been getting very hot lately, but this leak does not seem to be coming from the heater core. Any thoughts, suggestions before I spent $35-4500