When purchasing old used lenses I am always lucky to find well-oiled aperture blades. Over the years the oil will oxidize or polymerize which causes sticking of the thin metal blades due to capillary forces and friction.
There is just one solution. Unscrew the lens till the aperture. Take all collaborating parts out and submerge in alcohol. Most of the oil will be solved. Additional rubbing with a Q-tip helps this process. When everything is clean do not add new oil now. Just reassemble in reverse order and readjust diaphragm settings if needed.
When you have the above mentioned lens, follow these steps:
On the camera side remove three screws and lift the lens mount. Next release the aperture number ring and save the small ball and spring.
Remove the three screws around the inner cylinder and one of the manual aperture depth of field button. Pull the cylinder out of its housing, but first remove the spring and the button.
On the front turn the outer retaining ring anti clockwise and pull the lens compound out. There also comes a spacing ring out. Behind that the aperture can be seen.
Now try to find your finest screwdriver to release the aperture.
Submerge in alcohol (methylated spirit) and clean hearty. Put the blades back and check whether they move smoothly.
Get the aperture right back into the tube but do not tighten the screws as you have to adjust the aperture settings by its angle. Nevertheless you can put the lens compound back in its place. In the housing examine the aperture setting from fully opened at f/2.8 and closed down to f/22. Now tighten the aperture screws and finally mount the whole optical part in the housing. Fine adjustment of the aperture is still possible with the ramp which pushes against the aperture lever when setting the value by turning the ring.
Accessing single front lenses
For cleaning purposes, the front lenses can be released from – the front. How? At first unscrew (anti clockwise, as usual) the hidden ring with engraved lens name and serial number using your fingers. Underneath again two retaining rings appear. To turn them I use a fine scissors that fits the small gaps on each ring, tweezers will also do the trick. Then the lenses should come off easily.
After cleaning, it is a little tricky to find the right gang for the rings. It helps to turn first anti clockwise till it snaps correctly in and then tighten clockwise. Make sure the ring is horizontal and do not use to much force to prevent any damage or stuck.