The friction point is likely to be rather far from where oil can get from the outside.
I just popped mine out of the mount to work out the details. You don't really need a spanner wrench, a stainless steel desk ruler worked for me.
Once you have the optical block out, you'll see all the aperture mechanism. There's a black lever that attaches the outer ring to a pin coming out of the inner ring that operates the iris. First make scribe marks to note the exact location of that lever, it has oblong holes that calibrate the exact aperture! Remove that lever, see that the inner ring moves with no binding when you slide the pin side to side. If it doesn't, you need to do a complete tear down, clean that ring, and reassemble. (Not fun.)
If the inner ring moves freely, you just proceed to remove the bronze spring and detent ball. (Don't loose the ball, probably metric, a pain to replace.) Lift off the aperture ring, clean mating surfaces thoroughly, apply smallest amount of light oil, and reassemble. You'll need to fine tune the location of the bronze spring to get the aperture marks to line up with the mark.
