Had a go today but was unhappy with the result. Was using Frustulia rhomboides which may have been the problem - never had much luck with it - will try again tomorrow.I would love to see if you, or 75RR, really see any difference between the the condenser oiled and dry. (With DIC that is... I know it can make a difference in brightfield).
Visually the difference in DIC between the condenser oiled and dry seems to be readily apparent, however capturing that difference with the camera is proving elusive.