Rubbing across the etching lightly with OOOO grade wire wool and WD40 won't harm it at all, and in fact is likely to bring it up a bit by removing any surface corrosion/dirt/dried oil/finger marks etc.
I have known people use toothpaste on etching to try and make it whiter, making use of the slight grittiness that toothpaste has.
Don't think it made much difference, but neither apparently did it do any harm!
Etching is more durable than you might think, otherwise it wouldn't still be there after 70 odd years!