This one looks good:

Gerade bei #eBayKleinanzeigen gefunden. Wie findest du das?

https://www.ebay-kleinanzeigen.de/s-anzeige/bsa-b31-primaerkettenkasten/1476738106-306-370?utm_source=sharesheet&utm_medium=social&utm_campaign=socialbuttons&utm_content=app_android

The seller did send me some extra photo's, see below. I am not that interested, I already have enough of these. Price is also ok, IMO.

email (option): wdmotorcycles@gmail.com

I have had more than a few genuine WW2 WD M.20 outer chaincase covers over the years, some with damage and others appearing good. The general comment from those whom I have asked to repair holes in some has been the metal is extremely poor quality steel. I had one in particular that looked good but discovered it was porous with a constant film of oil on the outside of the chaincase.

I suppose that is how it was at the time - if it did not require top quality material you did not get it.