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He is correct as corrosion is a problem in getting the unit apart. I doubt it would be as much as a new range however if just a few burners need replacing. A grinder burns through those little screws very quickly. You should get another estimate from someone or just leave it be and light the burner manually. There is nothing dangerous as any burner can be left on and the flame can go out whether the sparker works or not, so I don't see that as any issue.