Ok we need to know an answer on this?
Is it the solvent?
Is it a change in the bluing process?
I just retired 10 years ago from one of the top ten engineering groups in the world. Worked in the world headquarters engineering lab. We did R&D ne product development, life testing, accident investigations. We also did outside vendors product testing for reliability.
My point is I'm sure s&w has an r&d lab and your solvent manufacturer has a test lab too. There probably not talking when I think they should be?
I think if they did talk together then we would be better advised on what solvent to use? What solvents not to use?