Non Pressure Leaks
WARNING: This page is about a different car, the 2020 Jaguar XE and 2019 Jaguar XE. However, it is still accessible from the selected car via links, so may be relevant.
Any reduced fluid volume in the brake master cylinder reservoir may be caused by two types of none pressure external leaks
Type 1: An external leak may occur at the brake master cylinder reservoir cap because of incorrect positioning of the gasket and cap. Reposition cap and gasket
Type 2: An external leak may occur at the brake master cylinder reservoir mounting seals. Repair such a leak by installing new seals and make sure that the brake master cylinder reservoir retaining bolt is correctly installed