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:
Remove the six screws from the back side of the depth of field ring and lift it
Push this little piece of brass, a part of the automatic aperture mechanic, inside
Unscrew the focus unit
Pull it upwards
Remove the aperture adjustment, but before that mark, its position with a scratch
Unscrew the aperture number ring
Watch out for the tiny ball and spring
When lifting the cylinder with the upper lens attached, it reveals a lever plus an inner cylinder which was held in place by the shiny aperture adjustment you already tuck out
Slide the inner cylinder upwards and remove the lever and the plate underneath
Submerge the aperture blades and all facing parts in alcohol (ethanol – methylated spirit)
Get rid of all the residual oil with several q-tips
When the surface is clean, a squeaking noise will be generated – ready to get back into the lens
Now reassemble all components and check if moveable parts do not stuck
Mind this tiny brass piece which pushes against the aperture lever
It needs to be aligned right as it establishes mechanic contact with the automatic aperture pin on the lens mount
Congratulation, you are finished and ready for shooting!
The entire process of opening the lens in a video: