Window leaks are fairly common.
First, I would not use silicone. Use a good flexible sealant. Emphasis on good.
Second, clean out the old sealant and wipe the area to be sealed with some mineral spirits. Stay away from the stick on graphics.
Third, seal only the top and sides.
Are you sure that the leak is from around the window and not the window glass seal itself?
After you get it sealed up, and all is dry take a garden hose to it and verify that the leak has stopped.
Sometimes water leaks can be tricky to find.
Peace
Dave