I have some experience in oiling negatives. My results are mixed. All my experience is with 35mm. I have used both Kami SMF 2001 and Dow Corning 200 viscosity 100. The reason given for oiling negatives is varied. One source says that it changes the refraction index of the gelatin to match air or glass. The other opinion is that it changes the refraction of the air to match glass. I have no idea which opinion is correct. In the scanning industry the Kami fluid is used. The Dow Corning 200 fluid...viscosity 100 is the choice of Bob Pace. When I use the Kami, I get spots that have dried and this shows on the print. When I use the Dow Corning fluid...viscosity 100 I am always left with at least one tiny bubble on the negative. If you ever desire to see how sharp a circle can be on a print this will show you. The Kami is to be used with a special and pricey tape. This tape will not turn into goo as will other tapes when exposed to the Kami fluid. When you are done the negative can be lightly wiped with a Pec pad. If you use the Dow Corning 200 Fluid..viscosity 100 the reccomended cleaning is to dip the negative in three sequential baths of film cleaner and to hang up to dry. The negatives are handled with a tweezer.
If you have a negative that is used with either of theses fluids any marks or imbedded dust will most likely disappear.
For me this has been a technique that I have yet to master.
The fact that a printer of Bob Paces caliber recommends the Dow Corning 200 Fluid...viscosity 100 tells me right off the bat that it is capable of working well. I have used this in my Condit pin registered oil immersion carrier. I also have a matching punch and pin glasses..