Quote Originally Posted by Doug Thomson
Jim may well have a point, still my humble advice is to leave sleeping dogs to lie. A spot of what appears to be oil on one blade of the diaphragm does not suggest disassembly. If the lens is functioning well (that is the diaphragm operates smoothly and freely), and the lens is clean and fungus free, leave it be. Now should you need to clean the blades, Jim's advice is excellent. Be careful with acetone, though. Methanol, isopropanol, and ethanol are excellent cleaning agents that will not harm anything in your lens ... acetone isn't always so benign.
Those points are well taken, Doug.

As for whether or not it's oil, I'm pretty sure it is. I know that sometimes older lenses develop a high polish on some parts of the aperture blades that looks like oil (I have another enlarger lens that has that appearance). But this is definitely some kind of lubricant. Also, I've noticed a faint trace of lubricant on the ring surrounding the rear element of the lens. So my guess is that the seller applied a little oil to the lens and, perhaps, overdid it.