Just reviving this one as I tried it today, I fitted a new set of labella Low tension flats to one of my jazzes and played it for a while, then I took them off to clean the fretboard and adjust the truss rod, I wiped the strings with Vaseline and cleaned them with a clean cloth and refitted, you can’t feel the Vaseline at all and the difference in tone is considerably noticeable, a much warmer sound but not too dull, it’s what I was looking for so really pleased