Walls and Ceilings - water damage wall help

Recently I submitted a question regarding a wall repair nightmare! After replacing roof (not due to leak), window (due to seal failure) and a wall replaced in the window area I find myself back to water coming into the interior of my home onto MY NEW WALL! Upon closer examination of the exterior window sill we found hairline crack that had been filled in with some type of sealer. This may be my whole problem. Needing a new exterior window seal and re-sealing the exterior hairling cracks in the masonry construction. Can someone tell me how this is done and how costly it is? Are any of the contractors liable for continuing these jobs without fully checking the water leak location? Should the window contractor have forewarned me about the exterior window sill condition before installing the window? Any help is appreciated. Thanks.