If you go down the ebay route for a replacement high level brake light be aware not all have the same quality of sealing gasket.
Have now been through two replacements on my Z4, replaced the original red that had leds out for a clear ebay one, the gasket was very poor on this one and didnt pull up into the gap very well at the ends. It lasted a year before some of the leds failed. Bought another from seller placeorder19 on ebay and that came with a better gasket than the first one so those on offer on ebay are not all the same. I did have to shave the edges of the connector down to get it to plug into the cars connector. Once in it pulled into the boot lid far better than the earlier replacement and it sealed fine. So far so good with this one. Currently my seller is out of stock so it will be a lottery what you get with other sellers regarding the quality of the unit and their gaskets.