If the upstand defect is limited
When the water-entry point is confirmed, the defect is localised and the surrounding construction is sound, a reinforced local repair may be considered.
The SealForge Kit — £129.99 plus delivery brings together liquid repair material, separate fleece reinforcement, primer, catalyst and application tools.
Movement at the wall junction, widespread failure, uncertain diagnosis or unsafe access should be handled by a competent roofing professional.