Also, if your window leaks to the interior between glass and aluminum frame, it's usually because the exterior of the frame lacks 'weep' holes. (Or, the existing weep holes have become plugged with debris.)
3/64" to 1/16" works best for drilling weep hole along the bottom of the frame. Any bigger and the holes are noticeable. Any smaller and surface tension prevents the water from draining completely. (In some cases, simply enlarging existing weep holes solve the problem.)
Note: As a general rule of thumb, "water goes where it wants to." The key to effective leak prevention is making the water go where you want it to go.
