2000 Durango leak

I have a 2000 Durango 5.9L . Recently, I have noticed a spot of fluid on the driveway under the vehicle everytime I park for more than a half hour or so.
Its definatly water/anti-freeze. There are no visible signs of leakage from any hose, or anyplace under the hood that I can see. I have looked from under the vehicle and there is a constant drip coming from between the back of the oil pan and the front of the transmission. Its coming from up high but I swear, I can't see anything leaking from under the hood area.
I thought maybe the heater core might be leaking, but there are none of the usualy symptoms ie.....smell of anti-freeze, leakage in the cab area.
Performance wise, the car runs fine. Does not overheat or anything. So, I assume that the thermostat is good. Heats fine inside etc.... I just have to add water about once a week depending on how much I drive.
Any suggestions or advise on where to go from here would be of great help!
Thanks!
John

Sounds like it could be coming from around the head.I would take it down and have the cooling system pressure tested.That will tell you where it is coming from.Better to be safe than sorry.