andy
i have a large durant as well. i have never been certain whether it is original or not. it has the three stars and the made in Germany stamped in clearly just like my original one. it also has an old mirror with slight discoloration spots on it.
however it does not have one of the bolts fixed to the base (both can come out) and the join between the round mirror and the base is slightly different to the one on my car. It looks like it has been repaired where the original fixed bolt was - see photo. I bought it as an original but would need to have a couple of people see it and compare it with the mirrors on some cars before i would swear to it - hence it had sat on the wall for a long time being ignored. I originally bought it as a spare in case something happened to mine. i may let it go to a good cause but only after i work out if it is real or not