As consulting engineers, we often have building owner clients ask us to provide remedial designs for leaking curtain walls. In some cases, budget considerations and the client's need to maintain building operations during construction dictate that the repairs be installed from the exterior, to avoid the cost and disruption caused by disassembly and reconstruction of the curtain wall. This type of exterior repair approach generally relies on surface seals to block water penetration at the outermost plane of the wall. Various sealant manufacturers have recently developed extruded silicone sheets for use in surface seal repairs. These products work well on flat surfaces, but are not well adapted to sealing three-dimensional corner joints that occur in many curtain walls. This paper presents our experience at two recent projects working with contractors and sealant manufacturers in the design and implementation of custom molded silicone flashing shapes to seal window frame corners against water leakage.