It looks OK to me
Looking for militaria from 38. Batterie, Heeres Küsten Artillerie Regiment 977, also from 31, 32 and 36. Batterie.
I agree, looks fine. Often these do look very good for their age if well stored.
Looks good to me as well. As Ade said, these can be found in excellent condition if stored correctly.
Below is one I picked up over the summer at a local gun shop at a bargain. I initially thought the same thing as you, that it was too good to be true however upon closer examination it was authentic. Your's appears to be in even better shap than my example!
Considering the condition, you should be able to see clearly the original inspection stamps under on the reverse of the liner...
These liners almost always look this way. I say it is a good original.
As stated above, this is ok - and very nice................!