Why does oil leak from filter cap on Hybrid 2005 Escape? Filter was replace and new O rings installed, but still leaks

I bought the car used with 80,000 miles, had been dealer serviced.  I changed the oil and filter, required removal of canister and insertion of filter and new o rings.  The leak appears to be from the drain plug which screws into the filter housing and is removed with a hex wrench.  I torque it tight but slow leak continues when engine is running. Anyone else have this problem?