On my 1938 Borsigwalde that part is numbered; so I guess in your specimen it should be numbered too, but I realized that on K98's there are more than often exceptions. Maybe a lazy worker forgot to serialize this part that day, or simply this spring was swapped during a strip and clean session.
Anyway, since everything else seems OK, I wouldn't be concerned by this detail: by the pics this one is a nice Mauser. I would ask for more detailed pics of bolt #'s and stock markings, just to be more sure...
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