Recommended all the time on camera repair yahoo group: remove the optical groups above and below diaphragm. In most lenses, this is relatively "easy" if you know your way inside lenses. On some, it can be hard, especially with floating elements design (some 2/28 vivitars had them, some did not).
Flush the diaphragm with enough of lighter fluid (pure naphta or benzine, depending on your language). It's not completely oil free, but almost, and works great for diaphragm blades. It's what most repairers use. Zippo fluid is good enough for that, while Ronson fluid is slightly more oily. Or you can get cheaper cleaning benzine, some are just pure naphta. If you want to do a trourough job, you will have to remove the diaphragm assembly and clean it outside the lens, because with the former, eventually the problems might resurface again as the remaining grease gets back. For a most trourough job on old lenses, clean the helicoid, regrease it with something better (a lot of older lenses used lubricants that evaporate and also flow into diaphragm mechanisms over time). Simply cleaning the blades with a cotton swab is usually not enough, full flushing of the mechanism is what's needed if you don't want to disassemble it outright. Frantisek
