Prepare the window. Clean the window, including the frame. Scrape off any loose flakes of paint so the surface is free of any dirt, dust or debris. Close the window.
Apply Vaseline. Apply an even, generous layer of Vaseline along the areas of the window that are touching the frame when closed.
Add sealant. Squeeze silicone bath sealant out of the tube and onto the frame. Apply a heavier coat in the larger gaps. Make sure you have a tight fit and there are no open areas without sealant.
Allow drying time. Keep the window closed until the sealant has had time to dry. Refer to the sealant label for specific drying time.