5 bucks? Almost as lucky as I am.
The normal going rate is about 100$
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I recently dismantled a 50mm. It's rather different to other takumars. If you can, try removing the cap from behind and then the rear element. Because if you go the front route, you might to have to completly dismantle the lens. I had to remove everything to get into all the elements. I am not sure if you can get the cap off without taking the lens apart completly, but worth a try. It just screw off like a ordinary bottle cap, under it you will find the normal lockrings to remove the rear elements, which will let you get into the back of the aperture blades.
However, if the back of the blades is not enough, you will probably have to take the whole lens apart. Which is nice, because then you can clean it all up and relubricate it. Mine had mould in the heli.