A frequent problem with this lens is the slow aperture, even when no oil is on the aperture blades. So, here how I disassembled and cleaned this lens.
remove the lens text ring.
remove the front group.
Detailed view with removed front group.
The back, and the bayonet must be removed.
Also the next ring which controls the aperture setting must go, as well as the small part with screws acessable from the front.
Remove the aperture ring, but don't let the small spring loaded ball fly through the room.
Remove the next ring (3 screws).
Remove the spring at the arrow, before it drops out unnoticed, and the aperture lever mechanism.
This should come out.
Now the aperture blade assembly can be removed, the red marked area should be free from grease and oil, if not, clean it !
The aperture blade parts, and in this sample, the blades are clean from oil.
But these parts are not free from oil/grease, so clean them !
Put in the aperture blades.
Then the first part.
And the next ring (you will need patience, the positioning of the rings and blades is tricky), and fix them with the three screws.
Then slide in, and fix this small part.
And here it is mounted again.
Mount the aperture pin mechanism with its spring.
Make sure the inside looks like this again.
Mount the small spring and the next rings, it probably won't stay put, but that can be fixed later .
Here the next ring, with the three screws, is mounted .
Make sure the aperture setting mechanism looks like this again.
Time to put back the aperture ring, but do not forget the springloaded ball.
And now the back only needs the bayonet part.
Blow away any dust, before putting the front group back in.
Lens text ring back in, and now the aperture is as snappy as it should be.