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. In this case, the main problem was accessable by only removing the bayonet part.
First a look at a sample which has no problems.
Notice the black coating on the inside of the bayonet part, this is very unusual for a K mount lens. This is probably done to reduce the friction of the aperture part which slides in a groove of this ring.
Another sample of this lens type, which suffers from a slow aperture. Notice the oil/grease, this must be cleaned so the ring with the aperture pin can move free !
Here, the groove also has oil/grease on it and must be cleaned, the aperture pin should move as frictionless as possible.
After removing the oil and grease behind the bayonet ring, this sample did not need further disassembly, but I have had samples which had also oil deeper in the aperture mechanism. The lens is very similar to the PENTAX-M 1:2.8 28mm Version 1, so look there for an impression of what to do.