Very few Nikkors have issues with the aperture, one with moisture on the blades is the Micro Nikkor 55mm 2.8 Ais, cheapest is to find another sample that is clean sample...
There can be many reasons, latest I saw a lens that had impact damage to the ring so it would turn really tightly...
It can be from earlier diy project gone bad,,,
It is very different from lens to lens how to get to thee aperture, some, a few are 10 min work others take for hours.