Ford Boss has 2 or 3 videos discussing the problem.
An O-ring is the problem. Last I heard, the replacement actuators he put in are leaking after a time too! Sounds like this is going tobe a widespread problem.
How you fix it depends on your warranty status. It is a b$"#*% to remove. Moreover, they changed the design so replacement would require reprogramming the AWD module if you have a MY2020 or early MY2021.
Me? I was past powertrain warranty and no ESP. I suspected the leak was a low pressure oil leak. I cleaned the area with brake cleaner (engine cold) then applied quick setting gasket sealer with my finger. The top surface you don't have access to, so I cleaned it again and sprayed Permatex leak sealer spray with straw (multiple coats). So far so good.