Bruce,
I think you are missing my point.
I set up spectro analysis on a small fleet of DC-6Bs way back in 1974, and it was so effective that we could tell who had been using fast idle on #4 to boost cabin ground cooling.(High Si)
Thing is, it is not normal to check for Sulphur which is not an expected wear product. This was the clue for NASA.
How frequent are scheduled Borescope checks? What is the interval?
I am aware of blade contamination from sulphur products in fuel (and additives eg water methanol in turbo-props) We used to walnut shell blast compressors for salt air contamination. Volcanic ash was not among the contaminants we used to to deal with. What are the procedures?