Questions about how to calk leak in window

[Jeff Norris]

Ok, so I've got water coming in the outside of my window. Notice how it is under the window frame and not through the window. It is not a fast leak as it took about a year after we paint for us to show up.

Now, this is how the corners of the window look on the outside (the right side is one is the one that is leaking). The siding here was replaced almost 3 years ago before we bought the house.

This is what other windows in the house look like.

Now my questions are:
1. How do I need to caulk this to prevent the leak
2. Do I need to do anything inside the house to the drywall that has gotten wet? All I can see is the part where the paint is showing the moisture coming through.

Thanks in advance,
Jeff