Hah! I'm driving round in Spikey's car (back up the thread) these days and literally just replaced that bit of card he mentioned holding the holder shut with a new clip… £25 delivered from ebay.
Armin if you're looking for a sunglasses holder there's a guy here https://www.facebook.com/groups/BMWZ4BUYANDSELL (Maz Cool) who had one a couple of weeks ago (he wanted £200 for it) came out of a fairly low mileage Z4M. My guess is he's still got it at that price. As you prob know these days they sell for around £400. If you can find one. And lots of sunglasses don't even fit!
If you only need the clip there's somone selling them on ebay for £20 + postage. An obscene amount of money for a tiny bit of plastic, but not as obscene as the cost of the entire holder. https://www.ebay.co.uk/itm/134413481379