I would start there. Replace the mechtronix sealing sleeve an the adapter. You have to remove the valve body in order to replace the adapter if I remember correctly. As for the sleeve its rather the easy part. Also change the filter an pan while you there. I think some one did a DIY on this.
13 740LI W/Msport package. Executive Package
DRIVER ASSISTANCE PKG, HUD,
OYSTER; NAPPA LEATHER SEAT TRIM,
Lane departure, blind spot detection,
Side & Top View Cameras
Aftermarket Rear entertainment