While I was changing the light bulb I found the reflector unit was loose in the housing. The reflector is held by three ball joints. The one on the upper side in the middle position is a metal ball in a nylon base, the most solid of them three. The right one is from nylon, it likes to pop out when something to the right bulb is done. The left one is nylon as well, logically it likes to pop out when something to the long beam bulb is done. On my headlight unit this seems the weakest ball joint.
The joints can be reconnected. This is best done with the headlight unit dismantled from the motorcycle. To get to the headlight it suffices taking the front bolts of the screen mounting off.
The headlight casing is held by two torx head bolts on the sides.
Now the headlight can be pulled from a pin on the rear of the radiator. There are three cables, one for the main lights and one for the parking light, and another cable is for the display. Pull them off.
That's the upper ball joint
and here the left one, which has disconnected in my case. Very hard to see and to reach:
(Right ball joint: sorry not available, the photo of the right ball joint was blurry)
The left ball joint is the hardest to come by. For bringing it back into it's seating pan successfully, I found it easier popping the right ball joint off as well. This way there is more free movement possible. Furthermore, before a reconnecting is attempted, the left ball needs to be adjusted into a favourable position by adjustment with the lights up-down adjuster. You will see the black ball appearing (if it is not already visible), if you eyeball from over the top of the headlight casing through the long beam bulb hole, into the direction where the spring of the adjuster mechanism is located. The best position of the black ball I found is when it just fully appears in the line of sight when viewed over the edge of the bulbs hole.
You need to grab into the two bulb holes now, which means touching the reflector surface. This should only be done with soft lint free cotton gloves. The reflector surface is extremely sensitive. It will still suffer a little in the process, depending how hard it is touched. And here, plus in the complexity of the entire process lays probably the reason why BMW exchanges the entire headlight unit with a new one, should the customer come with disconnected ball joints into the workshop.
Grab the lens with the pointing fingers through the bulb holes and direct the left pan over the ball. With a lot of sweat it eventually will snap-in. After the left ball joint has snapped into into correct position, the right side needs to be reconnected. This is not as hard. For achieving this successfully I found it easier bringing the lens with the left-right adjuster almost completely to be retracted to the right. After this eventually has worked out well, readjust the lens with the left-right adjuster, so the lens is aligned in parallel with the front glass.
Now check if any particles have dropped into the casing. If so, a vacuum cleaner will do good service getting it out. Might be advisable to do a vacuum anyway. The bulbs can now be replaced. Take note: One needs to be extremely careful to not disconnect any of the ball joints again, e.g through applying pressure when re-attaching the clips or the bulb plugs.
I don't think the reflector and the ball joints will stand this treatment endlessly. It is the truly most mysteriously engineered headlight I ever had on any bike. Mine did get the treatment for the second time by now.
