101% agree with replacing the radiator cap...do not go by what it on there currently as it could be wrong one.

On a side note....you can replace the oil pan gasket, front cover, rear main seal without pulling the engine out. If yours is a 4wd model, then the front diff has to come out first...not all that difficult. If a 2wd model....much, much easier to do these gaskets.

 

After a year of adding water periodically, my coolant leak mystery has been solved. Turns out it was a slow leak in the radiator that did not reveal itself until yesterday when I walked out of the car and heard a hissing sound. Steam coming out. Was not a slow leak anymore!
The leak was on the top of the radiator near the upper hose so I suppose that explains why there was never a puddle underneath.

 

I would continue to closely monitor the coolant level. At that amount of loss , you could have more than one leak. You could have a slow leak at the water pump for example. That can be hard to see sometimes. The intake manifold leak could be burned up in the combustion chamber and not visible from the exhaust.