Mysterious Coolant Leak

I have a 98 Voyager. 3.3 liter engine. 2 winters ogo it started leaking coolant. I thought it was a head gasket. I was putting in a gallon of coolant about every 30 miles. Didn't have the money to fix at the time, so I just kept pouring in coolant. It got to the point where I knew exactly when to put it in just by the mileage. Then one day I went to put some in and it was almost full. There was no puddle under the van either, when there was before. I took the van to the local Chrysler dealer and had them pressure test it. It tested fine, and did not leak any more. Now, 2 yrs later it has started doing the same thing.I'm puzzled. It looks like it is running down the front of the engine, just alittle off center to the right. No water in oil, and no oil in water. No steam, just a leak. Could this be a freeze out plug?