Generally, windows are fixed on the wall after the masonry work is complete. While doing so, a gap is bound to exist between the window frames and masonry. This gap may widen with time, creating all sorts of leakage problems. After a detailed inspection, apply Dr. Fixit Silicone Sealant in these gaps. Dr. Fixit Silicone Sealant is highly flexible which accommodates any movements caused by thermal expansion & contraction and is UV resistant.
You can use Dr. Fixit CrackX Shrinkfree for sealing plaster cracks up to 10 mm. It is a nonshrink crack filler and is easily paintable over to match the shades of the wall.