In my opinion
leave scabbard as is
It is an old knife that will I assume never be used as a knife nor carried so no need to make the scabbard what it isn’t also if you resell later the scabbard will look new and bring age of blade into question
Cleaning the blade and etching it will enhance though and be fully reversible.
Did you add washing up liquid to the hot vinegar as it breaks up surface tension in the vinegar and leads to a more even spread of liquid on the blade
Ps lovely item
Regards
Ken
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