There are a couple different places your windows can leak from.
It could be the seal between the window and frame, but most likely it is the seal between the frame and hull. The grey strip around the inside of the window is more of a beauty ring and will do nothing to stop leaks.
Remove the screws and pull the retaining ring from the inside of the window. From there you will see how to remove the window completely from the boat.
Once removed, clean off ALL the old caulking.
Go buy some butyl tape caulking at the marine store and use that to re-caulk your windows.
Some folks prefer 5200 or 4200 but that will make servicing them more difficult in the future.
Good luck fellas.