Morning Clive
Welcome to the Forum
Have you been in touch with BMW UK ? Dealers can vary massively in their approach and attitude with an issue like this.
I would take some advice on where you stand with the Sale of Goods Act and Consumer Rights amendments. As you have clear Internet evidence that this is a well know issue plus your own video of you draining water from your car, I would write to BMW UK (attaching all links to video) with a copy sent to the MD of your dealership (if you haven't already) I would ask for a time line for BMW/Ocean to resolve the issue to your satisfaction as it is a well documented problem supported by a service bulletin.
Good Luck and keep us posted
Dave