Unscrew the button or screw that retains the handle in position, eliminate the handle, then unscrew or get rid of address plate. This exposes the system and spindle. If there is water in the best of spindle along with the outer body is wet, it’s a sign the O-ring is leaking.  https://blocked-drains49405.blog-a-story.com/15555144/a-simple-key-for-roof-leak-repair-unveiled