Presumably, this lens doesn't have a shutter, so you're only talking about cleaning the aperture blades and mechanism. If you're confident about such things, you can disassemble the diaphragm and flush it with naphtha, taking particular care to note how the blades are assembled and how they overlap. This only applies to metal parts (which I think these diaphragms are--I haven't had to clean mine yet). If there are layers of paper or vulcanite blades (unlikely), don't soak these in naphtha.
Usually the blades have pins and these pins move in slots that are in an adjustment ring, and it's the friction between the pins and the slots that make the aperture stiff (unless there is something like oil on the blades). If the entire thing is made of metal, you might be able to get away by soaking the whole diaphragm assembly in a solvent without taking it apart (and saving the sometimes difficult task of reassembling the blades). If it's necessary to lubricate the pins, you can use a light grease. It probably isn't necessary to lubricate the diaphragm blades, but if you want to, you could use a dry graphite powder lubricant.
