Feel around the edges of the window frame on a windy day to detect air movement.
Cheap 100% silicone from a hardware store (hard to tool), acrylic caulk (shrinks), or expanding foam (can bow the frame). how to reseal a window fixed
Do not use cheap interior latex caulk for an exterior window project. It will fail within months. Choose one of the following: 100% Silicone Sealant Feel around the edges of the window frame
Dust and dirt prevent adhesion.
Inspect your window seals every autumn. Catching a small hairline crack early allows you to make a spot-repair before water penetrates your walls. acrylic caulk (shrinks)
Depending on the type of repair, you may need: